Gas Detector Units Explained: ppm, ppb, %LEL & %Vol

2026-09-16 Gas Nose 0 Comments

Gas detector specifications are full of units:

ppb
ppm
%LEL
%Vol

A CO detector may measure 0–500 ppm.

A VOC instrument may measure down into ppb.

A combustible gas monitor may display 0–100% LEL.

An oxygen or process-gas analyzer may display %Vol.

These units are related, but they do not all describe gas concentration in the same way.

The most important distinction is:

ppb, ppm and %Vol express actual gas concentration at different scales. %LEL expresses a combustible gas concentration relative to that gas’s lower explosive limit.

This is why:

10% LEL does not mean 10% gas by volume.

For methane, a detector showing 10% LEL may correspond to approximately 0.44–0.50%Vol methane, depending on which methane LEL reference the instrument uses.

Understanding these units is therefore not just a mathematical exercise. It affects:

detector selection
measurement range
alarm interpretation
calibration
combustible-gas safety
process monitoring

ppm vs ppb vs %LEL vs %Vol: Quick Comparison

Unit	Meaning	What It Describes	Typical Applications
ppb	Parts per billion	Very low actual concentration	Trace VOCs, environmental monitoring
ppm	Parts per million	Low actual concentration	CO, H₂S, NH₃, Cl₂, VOCs
%Vol	Percent by volume	Higher actual concentration	O₂, CO₂, process gases, biogas
%LEL	Percent of Lower Explosive Limit	Relative flammability level	Methane, hydrogen, propane and combustible gases

A useful shortcut is:

ppb = trace concentration
ppm = low concentration
%Vol = higher absolute concentration
%LEL = combustible-gas safety scale

But the correct unit depends on the measurement objective, not simply the gas name.

ppm, ppb and %Vol Are Different Scales of Concentration

Gas Concentration Scale: ppb, ppm and %Vol

For gases, instruments normally use ppm and ppb as volumetric or molar-fraction concentration units, even though the display often simply says ppm rather than ppmv.

The core relationships are simple:

1 ppm = 1,000 ppb

and:

1%Vol = 10,000 ppm

Therefore:

1%Vol
= 10,000 ppm
= 10,000,000 ppb

Industrial Scientific’s current gas-detection glossary uses the same relationship: 1 percent by volume = 10,000 ppm, while 100% volume corresponds to 1,000,000 ppm.

See: Industrial Scientific Gas Detection Glossary

What Does ppm Mean in Gas Detection?

ppm means:

parts per million

One ppm represents one part of the target gas in one million parts of the gas mixture.

For volume concentration:

1 ppm = 0.0001%Vol

Examples:

ppm	%Vol
1 ppm	0.0001%
10 ppm	0.001%
100 ppm	0.01%
1,000 ppm	0.1%
5,000 ppm	0.5%
10,000 ppm	1%

ppm is convenient when the hazardous or relevant concentration is too small to express clearly as a percentage.

For example:

25 ppm CO

is much easier to understand than:

0.0025%Vol CO

Why Are Toxic Gases Commonly Measured in ppm?

Many toxic gases can become important at concentrations far below one percent by volume.

Examples include:

carbon monoxide — CO
hydrogen sulfide — H₂S
ammonia — NH₃
chlorine — Cl₂
sulfur dioxide — SO₂
nitrogen dioxide — NO₂

That makes ppm a practical display scale.

This does not mean:

ppm is inherently more accurate than %Vol.

It simply matches the concentration range better.

A toxic-gas detector might have a range such as:

0–100 ppm

while a process analyzer for another application could measure the same gas at a much higher concentration using %Vol.

The unit should make the relevant concentration range easy to interpret.

What Does ppb Mean?

ppb means:

parts per billion

It is one thousand times smaller than ppm.

1 ppm = 1,000 ppb

Therefore:

1 ppb = 0.001 ppm

Examples:

ppb	ppm
1 ppb	0.001 ppm
10 ppb	0.01 ppm
100 ppb	0.1 ppm
1,000 ppb	1 ppm
10,000 ppb	10 ppm

ppb is particularly useful for:

trace VOC monitoring
environmental monitoring
semiconductor contamination
ultra-low toxic-gas measurement
high-sensitivity PID applications
analytical instrumentation

Is ppb More Accurate Than ppm?

No.

This is an important misunderstanding.

A smaller display unit does not automatically mean a better instrument.

Consider two hypothetical sensors:

Sensor A

Range:

0–100 ppm

Resolution:

0.1 ppm

Sensor B

Range:

0–5,000 ppb

Resolution:

100 ppb

Sensor B uses ppb, but that alone tells you nothing about whether it is:

more accurate
more stable
more selective
faster

You still need to evaluate:

accuracy
resolution
detection limit
repeatability
drift
cross-sensitivity

So:

Smaller unit ≠ better sensor.

What Does %Vol Mean?

%Vol means:

percent by volume

If methane concentration is:

1%Vol

then methane makes up approximately 1 volume unit for every 100 volume units of the mixture.

The conversion is:

ppm = %Vol × 10,000

and:

%Vol = ppm ÷ 10,000

Examples:

0.01%Vol = 100 ppm
0.1%Vol = 1,000 ppm
0.5%Vol = 5,000 ppm
1%Vol = 10,000 ppm
5%Vol = 50,000 ppm

This relationship is straightforward because ppm and %Vol are simply two scales for expressing volume fraction.

Why Is Oxygen Usually Displayed in %Vol?

Normal atmospheric oxygen is approximately:

20.9%Vol

It could mathematically be expressed as approximately:

209,000 ppm

but that would be unnecessarily awkward.

%Vol is simply a much more useful scale.

The same principle applies to high-concentration process gases.

Typical %Vol applications include:

oxygen
high-concentration CO₂
methane in biogas
hydrogen process gas
pipeline purging
inerting
gas blending

RKI’s current technical FAQ similarly distinguishes %LEL as a combustible-safety scale and %Vol as an absolute concentration scale used for applications such as purging and inerting.

See: RKI — %LEL vs %Vol

%Vol Is an Absolute Concentration Scale

The easiest way to distinguish %Vol and %LEL is:

%Vol

asks:

How much gas is actually present?

%LEL

asks:

How close is the combustible gas concentration to its lower explosive limit?

This is a fundamental difference.

If a methane analyzer reads:

2%Vol CH₄

that means methane represents approximately 2% of the gas mixture by volume.

If a combustible monitor reads:

40% LEL

you still need to know the methane LEL reference used by that instrument before converting the reading to %Vol.

What Does %LEL Mean?

LEL means:

Lower Explosive Limit

It is also commonly called:

Lower Flammable Limit — LFL

Below this concentration, the fuel-air mixture is generally too lean to sustain flame propagation under the defined test conditions.

A combustible detector commonly displays:

0–100% LEL

This does not mean:

0–100% gas concentration.

Instead:

0% LEL

means the instrument is at the bottom of its %LEL combustible scale.

It should not be interpreted as proof that absolutely zero combustible gas molecules are present.

50% LEL

means the concentration is half of the applicable LEL reference.

100% LEL

means the gas concentration has reached the applicable lower explosive limit.

This is why:

100% LEL may represent only a few percent gas by volume.

The Biggest Mistake: 10% LEL Is Not 10%Vol

Suppose we use a methane LEL reference of:

5.0%Vol

Then:

100% LEL = 5.0%Vol methane

Therefore:

50% LEL = 2.5%Vol

20% LEL = 1.0%Vol

and:

10% LEL = 0.5%Vol

Since:

0.5%Vol = 5,000 ppm

we get:

10% LEL methane
= 0.5%Vol
= 5,000 ppm

But there is an important qualification.

5.0%Vol is not the only methane LEL reference used by gas detection instruments.

Why 10% LEL Methane Can Mean 4,400 ppm or 5,000 ppm

This is one of the most important details in combustible-gas measurement.

Dräger’s current PIR 7000 documentation supports different LEL calculation categories.

For methane it lists, among others:

NIOSH-Based Reference

Methane LEL = 5.0%Vol

Therefore:

10% LEL
= 0.50%Vol
= 5,000 ppm

IEC-Based Reference

Methane LEL = 4.4%Vol

Therefore:

10% LEL
= 0.44%Vol
= 4,400 ppm

Dräger’s current methane reference page likewise lists 4.4%Vol LEL while specifically noting that 5%Vol is commonly used in North America.

See:

This leads to a very important rule:

Never convert %LEL to ppm until you know the target gas and the LEL reference used by the detector.

The image above therefore shows two valid calculation examples, not two different physical methane concentrations for the same definition.

General Formula: %LEL to %Vol

Suppose:

L = gas LEL in %Vol

and:

X = detector reading in %LEL

Then:

Gas concentration (%Vol)
= (X ÷ 100) × L

For example:

Methane LEL reference:

5.0%Vol

Detector:

20% LEL

Then:

(20 ÷ 100) × 5.0
= 1.0%Vol

General Formula: %LEL to ppm

Once you know the %Vol concentration:

ppm
= %Vol × 10,000

So the combined equation is:

ppm
= (%LEL ÷ 100)
× LEL (%Vol)
× 10,000

Example:

Methane LEL = 5.0%Vol
Reading = 10% LEL

ppm
= 0.10 × 5.0 × 10,000
= 5,000 ppm

But again:

The calculation is only as correct as the LEL value you put into it.

How Do You Convert ppm Back to %LEL?

If the gas concentration is already known in ppm:

First:

%Vol = ppm ÷ 10,000

Then:

%LEL
= Gas concentration (%Vol)
÷ Gas LEL (%Vol)
× 100

For example, using a 5.0%Vol methane LEL:

5,000 ppm
= 0.5%Vol

Then:

0.5 ÷ 5.0 × 100
= 10% LEL

Why %LEL Is Gas-Specific

Different combustible gases have different lower explosive limits.

Therefore the same:

10% LEL

does not represent the same absolute concentration for every gas.

Conceptually:

Gas A

LEL = 4%Vol

10% LEL = 0.4%Vol

Gas B

LEL = 2%Vol

10% LEL = 0.2%Vol

Both are:

10% LEL

because each has reached 10% of its own flammable-limit reference.

This is the purpose of the unit.

%LEL normalizes different combustible gases to a flammability-risk scale.

Why Use %LEL Instead of ppm for Combustible Safety?

Suppose two gases are each present at:

5,000 ppm

Gas A may still be far below its LEL.

Gas B may be much closer to its LEL.

The ppm value tells you:

How much gas is present?

But %LEL tells you:

How far has the atmosphere progressed toward the gas’s flammable concentration?

That makes %LEL much more intuitive for combustible-gas safety.

This is why standard multi-gas safety monitors often show:

O₂ → %Vol
combustible gas → %LEL
H₂S → ppm
CO → ppm

For more on combustible risk, see What Is a Safe LEL Level?.

%LEL Does Not Measure Toxicity

This distinction is essential.

A gas can present a toxic exposure hazard long before it reaches a significant fraction of its LEL.

Benzene is a classic example.

A combustible-gas detector can correctly show a very low %LEL reading while occupational exposure is already significant.

Therefore:

%LEL describes flammability—not toxicity.

This is why industrial environments sometimes require both:

LEL monitoring

and:

ppm-level VOC monitoring

For a detailed example, see PID vs LEL Gas Detector: What’s the Difference?.

The Same Gas Can Be Measured in ppm, %LEL and %Vol

The unit is determined by the measurement objective.

Consider hydrogen.

Small Hydrogen Leak

Goal:

find an early low-concentration leak.

Possible unit:

ppm

Hydrogen Explosion Safety

Goal:

determine whether hydrogen is approaching a flammable concentration.

Unit:

%LEL

High-Concentration Hydrogen Process

Goal:

measure hydrogen as a major component of the gas mixture.

Unit:

%Vol

The same logic applies to methane.

Methane Leak Survey

May use:

ppm

Methane Safety Monitor

Typically uses:

%LEL

Biogas Analyzer

May use:

%Vol CH₄

So:

Same gas. Different range. Different measurement objective.

The ppm ranges shown in the illustration are conceptual examples only. Actual instrument ranges depend on sensor technology and application.

Why This Matters in Wastewater and Biogas

A wastewater facility provides a very good real-world example.

A portable worker-safety detector may monitor methane as:

0–100% LEL

But an anaerobic digester analyzer may measure:

CH₄ in tens of %Vol

These are not interchangeable instruments.

The first asks:

Is the surrounding atmosphere becoming flammable?

The second asks:

What fraction of the process biogas is methane?

For more, see Wastewater Gas Detection: What Gases Should Be Monitored?.

Why This Matters for Hydrogen Applications

The same issue appears in:

electrolyzers
hydrogen storage
fuel cells
battery rooms

A low-level hydrogen sensor may be selected for:

early leak detection

while a second detector or measurement range is used for:

%LEL safety

and process equipment may require:

%Vol hydrogen

Selecting a sensor simply because its datasheet says:

Target Gas: H₂

is therefore not enough.

You need:

Gas + Range + Unit + Measurement Objective

Unit Is Not the Same as Range

Consider a hypothetical CO detector:

Unit

ppm

This tells us how concentration is expressed.

Range

0–500 ppm

This tells us the minimum-to-maximum measuring span.

Resolution

1 ppm

This tells us the smallest display increment.

Low Alarm

Configurable

This is a safety action threshold.

High Alarm

Configurable

Another action threshold.

These specifications are completely different.

So:

Unit ≠ range ≠ resolution ≠ alarm.

Unit Is Not the Same as Accuracy

A detector may display:

1 ppm resolution

That does not mean its accuracy is:

±1 ppm

For example, an instrument could display:

38 ppm
39 ppm
40 ppm

while having a specified measurement accuracy larger than one ppm.

Resolution simply describes the smallest displayed or reported increment.

Always check:

measuring range
resolution
accuracy
repeatability
response time
lower detection limit

separately.

Unit Is Not the Same as Alarm Setting

A combustible detector might have:

Range: 0–100% LEL

but the Low alarm may be configured far below:

100% LEL

Likewise:

CO sensor range: 0–500 ppm

does not mean:

High alarm = 500 ppm

Alarm values are selected from:

applicable exposure criteria
risk assessment
site procedure
detector capability

For the complete explanation, see Gas Detector Alarm Settings: Low, High, STEL & TWA Explained.

Measurement Unit Is Not the Same as Sensor Technology

Another common mistake is assuming a unit automatically identifies the sensing principle.

For example:

Electrochemical

Commonly used with:

ppm

but that does not mean every ppm sensor is electrochemical.

Catalytic Bead

Commonly displays:

%LEL

NDIR

Depending on the design, may measure:

ppm
%LEL
%Vol

PID

Commonly displays:

Thermal Conductivity

Often used for:

high-concentration %Vol

The current Dräger PIR 7000 platform is a good illustration: depending on configuration, the same infrared platform can use %LEL, %Vol or ppm measurement units.

So:

Unit describes the measurement result—not the sensor principle.

Can One Detector Automatically Switch From %LEL to %Vol?

Some specialized instruments can.

This is useful in applications where gas concentration can move from:

low combustible-safety range

into:

high process concentration

RKI, for example, describes dual-range instruments that use a catalytic sensor for %LEL and a thermal-conductivity sensor for high %Vol measurement.

This highlights an important point:

A detector that measures 0–100% LEL is not automatically capable of measuring 0–100%Vol.

Those ranges can require different sensing technology.

Why Calibration Gas Matters for %LEL

A combustible detector may be calibrated using:

methane
pentane
propane
another specified gas

But catalytic sensors do not necessarily respond equally to every combustible gas.

Suppose a sensor is calibrated with methane but is measuring another hydrocarbon.

Its actual response may differ.

Manufacturers may provide:

correction factors
correlation factors
gas-specific calibration options

This means:

A mathematically correct %LEL conversion does not automatically guarantee a physically accurate measurement.

You still need to understand:

calibration gas
target gas
sensor technology
relative sensitivity

For calibration fundamentals, see Gas Detector Bump Test vs Calibration.

Can Any %LEL Reading Be Converted Directly to ppm?

Not responsibly unless you have enough information.

You need to know:

What gas is being measured?
What LEL value does the instrument use?
What is the calibration gas?
How does the sensor respond to the target gas?
Is the atmosphere a single gas or an unknown mixture?

If the atmosphere contains an unknown hydrocarbon mixture, a simple conversion may produce a neat number without representing the real gas concentration accurately.

This leads to an important engineering principle:

Mathematical conversion is not the same thing as measurement accuracy.

What About ppm vs mg/m³?

Another concentration unit frequently encountered in occupational hygiene is:

mg/m³

ppm and mg/m³ are not related by one universal fixed factor.

Why?

Because:

ppm

describes a volume/molar fraction.

mg/m³

describes mass per volume.

Conversion therefore depends on:

gas molecular weight
temperature
pressure

So unlike:

1%Vol = 10,000 ppm

you cannot say:

1 ppm = one universal mg/m³ value

for every gas.

CO, H₂S and chlorine all have different molecular weights and therefore different ppm-to-mass relationships.

Which Unit Should You Use?

A practical starting point is:

Application	Typical Unit
Trace environmental gas	ppb
Ultra-low VOC monitoring	ppb / ppm
CO worker safety	ppm
H₂S worker safety	ppm
NH₃ / Cl₂ safety	ppm
PID VOC screening	ppm / ppb
Combustible-gas safety	%LEL
Oxygen	%Vol
High-concentration CO₂	%Vol
Biogas methane composition	%Vol
Hydrogen process concentration	%Vol
Low-level H₂ leak	ppm
Hydrogen explosion protection	%LEL

This is not a rigid rule.

It is a way to match the scale to the measurement problem.

Choose the unit from the concentration range and safety objective—not from the gas name alone.

Choosing the Correct Measurement Unit

How to Choose a Gas Detector Measurement Unit

A simple decision process is:

Step 1 — What Gas Are You Measuring?

Identify the target.

Step 2 — What Concentration Do You Expect?

Is it:

trace
low concentration
near a flammable threshold
a major component of the gas mixture?

Step 3 — What Is the Measurement Objective?

Trace Monitoring

Consider:

ppb

Toxic / Low-Level Measurement

Consider:

ppm

Combustible Safety

Consider:

%LEL

High Absolute Concentration

Consider:

%Vol

Step 4 — Select Sensor Technology

Choose a sensor that can reliably measure the required:

gas
range
environment

Step 5 — Confirm Calibration Basis

Especially for combustible gases.

Step 6 — Configure Alarms

Alarm settings come after the correct measurement range and unit have been selected.

Measurement-Unit Selection Checklist

Before selecting a gas sensor or detector, confirm:

Target gas
Expected minimum concentration
Expected maximum concentration
Trace / toxic / combustible / process objective
Appropriate unit
Required measurement range
Required resolution
Accuracy requirement
Sensor technology
Target gas LEL where relevant
LEL reference convention
Calibration gas
Relative gas response
Alarm thresholds
Cross-sensitivity
Environmental conditions

For multi-gas instruments, see How to Choose Gases for a Multi-Gas Detector.

Frequently Asked Questions

What does ppm mean on a gas detector?

ppm means parts per million.

For gas detection it normally represents the volume or molar fraction of target gas in the surrounding gas mixture.

What does ppb mean?

ppb means parts per billion.

1 ppm equals 1,000 ppb.

How many ppm are in 1%Vol?

1%Vol = 10,000 ppm

Therefore:

0.1%Vol = 1,000 ppm

and:

0.01%Vol = 100 ppm

How many ppb are in 1 ppm?

1 ppm = 1,000 ppb

What does %LEL mean?

%LEL expresses combustible gas concentration as a percentage of the gas’s applicable lower explosive limit.

100% LEL means the concentration has reached that LEL reference—not that the atmosphere contains 100% gas.

Is 10% LEL the same as 10% gas by volume?

No.

For methane using a 5.0%Vol LEL reference:

10% LEL = 0.5%Vol methane

not:

10%Vol methane

What is 10% LEL methane in ppm?

It depends on the LEL reference.

Using:

5.0%Vol methane LEL

10% LEL = 5,000 ppm

Using:

4.4%Vol methane LEL

10% LEL = 4,400 ppm

Check the instrument configuration and applicable reference.

Why is methane LEL sometimes listed as 4.4% and sometimes 5%?

Different reference systems and historical test conventions use different values.

For example, current Dräger documentation supports a 5.0%Vol NIOSH-based methane reference and a 4.4%Vol IEC-based reference.

Can I convert %LEL directly to ppm?

Yes mathematically, but only after identifying the gas and applicable LEL value.

For practical detector interpretation, calibration gas and sensor response also matter.

What is the difference between %LEL and %Vol?

%Vol is an absolute concentration scale.

%LEL expresses a combustible gas concentration relative to that gas’s lower explosive limit.

Can the same gas be measured in ppm and %LEL?

Yes.

Hydrogen or methane can be measured in ppm for low-level leaks and %LEL for combustible safety.

The instrument range and sensor technology may be different.

Can methane be measured in %Vol?

Yes.

High-concentration methane measurements, such as biogas composition, are commonly expressed in %Vol.

Why is oxygen measured in %Vol?

Atmospheric oxygen exists at roughly 20.9% by volume, making %Vol a much more practical scale than ppm.

Why are toxic gases usually measured in ppm?

Many toxic gases become important at concentrations much lower than 1%Vol, so ppm provides a convenient scale.

When should ppb be used instead of ppm?

ppb is useful when the required concentration range is below the practical ppm scale, such as trace environmental or very low VOC measurements.

Is ppb more accurate than ppm?

No.

The unit does not determine accuracy.

Check the sensor’s stated range, accuracy, resolution and detection limit.

Is %LEL a toxicity measurement?

No.

%LEL describes flammability.

A substance may present a toxic exposure hazard at a concentration far below its LEL.

Is sensor range the same as measurement unit?

No.

For example:

ppm

may be the unit while:

0–500 ppm

is the range.

Is resolution the same as accuracy?

No.

Resolution is the smallest display increment.

Accuracy describes how closely the measured value represents the actual concentration.

Can ppm be converted directly to mg/m³?

Only after considering the specific gas and conditions such as molecular weight, temperature and pressure.

There is no universal ppm-to-mg/m³ factor for every gas.

Final Takeaway

The four common gas detector units answer different measurement needs.

ppb

Use when the concentration is extremely small.

ppm

Use for many low-level toxic and VOC measurements.

%Vol

Use when the gas forms a meaningful percentage of the mixture.

%LEL

Use when the question is:

How close is this combustible atmosphere to its lower explosive limit?

The key relationships are:

1 ppm = 1,000 ppb

1%Vol = 10,000 ppm

But:

%LEL ≠ %Vol

without knowing the gas-specific LEL.

That is the most important distinction.

A methane detector showing:

10% LEL

does not contain:

10% methane

and even the conversion to ppm depends on which methane LEL reference the instrument uses.

Therefore the most useful gas detector selection rule is:

Start with the gas, concentration range and measurement objective. Then choose the unit, sensor technology, calibration basis and alarms.

Do not select a gas sensor from the unit alone—and never interpret %LEL as if it were simply another name for %Vol.

References and Further Reading

Author

Gas Nose

8618037022596

Gas Detector Measurement Units: ppm vs ppb vs %LEL vs %Vol

ppm vs ppb vs %LEL vs %Vol: Quick Comparison

ppm, ppb and %Vol Are Different Scales of Concentration

What Does ppm Mean in Gas Detection?

Why Are Toxic Gases Commonly Measured in ppm?

What Does ppb Mean?

Is ppb More Accurate Than ppm?

Sensor A

Sensor B

What Does %Vol Mean?

Why Is Oxygen Usually Displayed in %Vol?

%Vol Is an Absolute Concentration Scale

%Vol

%LEL

What Does %LEL Mean?

0% LEL

50% LEL

100% LEL

The Biggest Mistake: 10% LEL Is Not 10%Vol

Why 10% LEL Methane Can Mean 4,400 ppm or 5,000 ppm

NIOSH-Based Reference

IEC-Based Reference

General Formula: %LEL to %Vol

General Formula: %LEL to ppm

How Do You Convert ppm Back to %LEL?

Why %LEL Is Gas-Specific

Gas A

Gas B

Why Use %LEL Instead of ppm for Combustible Safety?

%LEL Does Not Measure Toxicity

The Same Gas Can Be Measured in ppm, %LEL and %Vol

Small Hydrogen Leak

Hydrogen Explosion Safety

High-Concentration Hydrogen Process

Methane Leak Survey

Methane Safety Monitor

Biogas Analyzer

Why This Matters in Wastewater and Biogas

Why This Matters for Hydrogen Applications

Unit Is Not the Same as Range

Unit

Range

Resolution

Low Alarm

High Alarm

Unit Is Not the Same as Accuracy

Unit Is Not the Same as Alarm Setting

Measurement Unit Is Not the Same as Sensor Technology

Electrochemical

Catalytic Bead

NDIR

PID

Thermal Conductivity

Can One Detector Automatically Switch From %LEL to %Vol?

Why Calibration Gas Matters for %LEL

Can Any %LEL Reading Be Converted Directly to ppm?

What About ppm vs mg/m³?

ppm

mg/m³

Which Unit Should You Use?

Choosing the Correct Measurement Unit

Step 1 — What Gas Are You Measuring?

Step 2 — What Concentration Do You Expect?

Step 3 — What Is the Measurement Objective?

Trace Monitoring

Toxic / Low-Level Measurement

Combustible Safety

High Absolute Concentration

Step 4 — Select Sensor Technology

Step 5 — Confirm Calibration Basis

Step 6 — Configure Alarms

Measurement-Unit Selection Checklist

Frequently Asked Questions

What does ppm mean on a gas detector?

What does ppb mean?

How many ppm are in 1%Vol?

How many ppb are in 1 ppm?

What does %LEL mean?

Is 10% LEL the same as 10% gas by volume?