Nm3 vs m3: Conversion Formula and Chart for Japanese Specs

A burner package arrives from a Japanese supplier. The datasheet lists combustion air as 1,000 Nm³/h, the plant air header as 0.7 MPaG, and the instrument air consumption in L/min (ANR). Before you size a fan, a duct, or an air line, you need to know what those flow numbers mean at your actual temperature and pressure.

The short answer: Nm³ (normal cubic meter) is a gas volume converted to 0°C and 1 atm (101.325 kPa), so it measures how much gas there is. To get the actual volume in m³, multiply by a temperature ratio and a pressure ratio. Inside a 20°C, 0.5 MPaG (72.5 psig) air line, 1 Nm³ of air takes up only about 0.18 m³. Mix the two up and a pipe or compressor can be off by a factor of five or more.

This guide covers what Nm³ means and how Japanese engineers write it, the conversion formula and a quick-reference chart, how Nm³ differs from Sm³, ANR, and SCFM, worked examples for compressed air, combustion air, flue gas, and Japanese city gas, and a checklist and question list for the Japanese side.

Contents

1. What Is Nm3 (Normal Cubic Meter)?
2. Nm3 to m3 Conversion Formula
3. Nm3 vs Sm3, ANR, and SCFM
4. When to Use Nm3 and When to Use m3
5. Worked Examples: Combustion Air, Flue Gas, and City Gas
6. Checklist for Japanese Datasheets and Catalogs
7. Limits of This Guide
8. FAQ
9. Sources

What Is Nm3 (Normal Cubic Meter)?

Nm³ is a unit for the amount of gas: the volume the gas would occupy at atmospheric pressure and 0°C. The "N" stands for "normal," meaning a fixed reference state, and it is added to m³ (cubic meter).

On Japanese shop floors you will hear it read as norumaru-ryube (ノルマルリューベ). Ryube is the shop-floor reading of 立米, a short form of cubic meter, so the term simply means "normal cubic meter." There is no fixed way to write it: some documents use m³N (read ryube-norumaru) instead of Nm³. Flow rates are written Nm³/h (per hour) and Nm³/min (per minute).

A reference state is needed because gas volume changes with temperature and pressure. The ideal gas law shows the relationship, which is the same one behind Boyle's and Charles's laws:

Take 1 Nm³ of air. At atmospheric pressure and 0°C, it fills exactly 1 m³. Heat it to 100°C and it expands to about 1.366 m³. Double the pressure at 0°C instead, and it shrinks to 0.5 m³.

Figure 1: The Same 1 Nm³ of Air in Three States

The amount of air never changes. Only the space it takes up does.

Ideal-gas values. Pressures are absolute.

In all three states the air inside is the same. That is the point of Nm³: it tells you how much gas there is, not how much space it fills right now. In amount-of-substance terms, 1 Nm³ is about 44.6 mol, because 1 mol of an ideal gas occupies about 22.414 L at 0°C and 101.325 kPa (CODATA value).

Figure 2: Nm³ vs m³

Nm³ is an amount. m³ is the space the gas fills where it is.

Nm³ (normal cubic meter)

m³ (actual cubic meter)

What it measures

Nm³: amount of gas (proportional to moles and mass)

m³: actual volume at the local temperature and pressure

Reference state

Nm³: 0°C, 101.325 kPa (1 atm), dry gas

m³: local temperature and pressure

When temperature or pressure changes

Nm³: the number stays the same

m³: rises with temperature, falls with pressure

Typical uses

Nm³: combustion air, fuel gas amount and heat input, flue gas emission limits, blower and gas capacity ratings

m³: pipe and duct velocity, tank capacity, the air volume a fan actually moves

Flow units

Nm³: Nm³/h, Nm³/min, NL/min

m³: m³/h, m³/min, L/min

"Dry gas" follows the way fuel gas heating values are defined in Japan (per 1 m³ of dry gas at 0°C and 101.325 kPa). Some references, such as ANR for pneumatic equipment, include humidity.

Nm³ is an industry convention, not an SI unit. Strictly speaking, N is the symbol for the newton, so "Nm³" could be read as newton times cubic meter. SI style puts the measurement conditions on the quantity, not on the unit (NIST SP 811), and Japanese law, for example, writes out the condition in words ("converted to a temperature of 0°C and a pressure of 1 atm"). Even so, Nm³ is the common way to write it in industry.

Nm3 to m3 Conversion Formula

To convert between Nm³ and m³, multiply by a temperature ratio and a pressure ratio. Convert the temperature to absolute by adding 273.15 to °C, and convert gauge pressure to absolute by adding 101.325 kPa before you take the ratio.

The first line gives actual m³ from Nm³. The second gives Nm³ from actual m³. Decide which one you have before you pick a line. Rounding 101.325 to 101.32 or 101.3 barely changes the result.

If the direction is confusing, think about what happens physically: a higher temperature increases m³, and a higher pressure reduces it. The same formula works for flow rates. Enter Nm³/h and you get m³/h; enter Nm³/min and you get m³/min.

Figure 3: Five Steps to Convert Nm³ and m³

Check the reference state and the pressure type before you touch the formula.

STEP 01Check the basisIs the datasheet, flowmeter, or catalog value in Nm³, actual m³, or another basis such as ANR?

STEP 02Check the pressure typeMPaG and kPaG are gauge; MPa(abs) is absolute. Convert everything to kPa

STEP 03Go absolute°C + 273.15; gauge pressure + 101.325 kPa

STEP 04Multiply the two ratiosNm³ → m³: temperature ratio × pressure ratio. For the reverse, swap numerator and denominator

STEP 05Sanity-check the sizeCompressed air: m³ should be smaller than Nm³. Hot flue gas: it should be larger

A pressure gauge reads zero at atmospheric pressure. On the vacuum side (negative readings), add the reading to 101.325 kPa in the same way to get absolute pressure.

The most common mistake is forgetting to add atmospheric pressure to the gauge pressure. Here are three ways to calculate the pressure ratio for air at 0.5 MPaG:

Skip the pressure correction entirely and you overestimate the compressed-air volume about sixfold, which means an air line far larger than it needs to be.

The chart below gives ready-made factors from the same formula. Multiply a flow rate by the factor to convert it.

Figure 4: Nm³ to m³ Conversion Chart (Gauge Pressure × Temperature)

The three columns on the left give the actual m³ for 1 Nm³. The three on the right give the Nm³ in 1 actual m³ at each condition.

Gauge pressure	1 Nm3 → m3			1 m3 → Nm3
	0°C (32°F)	20°C (68°F)	40°C (104°F)	0°C (32°F)	20°C (68°F)	40°C (104°F)
0 (atmospheric)	1.000	1.073	1.146	1.000	0.932	0.872
0.1 MPa (14.5 psig)	0.503	0.540	0.577	1.987	1.851	1.733
0.3 MPa (43.5 psig)	0.252	0.271	0.289	3.961	3.691	3.455
0.5 MPa (72.5 psig)	0.169	0.181	0.193	5.935	5.530	5.177
0.7 MPa (101.5 psig)	0.126	0.136	0.145	7.908	7.369	6.898
0.8 MPa (116 psig)	0.112	0.121	0.129	8.895	8.289	7.759
1.0 MPa (145 psig)	0.092	0.099	0.105	10.869	10.128	9.481

Calculated as an ideal gas with atmospheric pressure at 101.325 kPa, rounded to three decimal places. Humidity is ignored. Example: 100 Nm³/h at 0.5 MPaG and 20°C is 100 × 0.181 ≈ 18.1 m³/h.

Reading the chart: in compressed air at 0.7 MPaG and 20°C, every 1 m³ of pipe volume holds about 7.37 Nm³. Pressure drives the factor. Temperature matters much less: a 20°C difference shifts it by about 7%. If you first check how many atmospheres the absolute pressure is, you will not be off by an order of magnitude.

Worked Examples: Compressed Air

Say 100 Nm³/h of compressed air flows through a line at 40°C and 0.5 MPaG (500 kPaG). The actual volumetric flow is:

Because the air is compressed, its actual volume is about one-fifth of the Nm³ figure. Use 19.3 m³/h when you calculate the velocity in the pipe.

Now the reverse. A line at 25°C and 0.7 MPaG (700 kPaG) carries an actual flow of 5 m³/min:

Brought back to 0°C and 1 atm, those 5 m³/min become 36.2 Nm³/min, about 7.2 times as much. Use this value when you compare the supply against the air consumption of equipment rated in Nm³/min.

Nm3 vs Sm3, ANR, and SCFM

Nm³ uses 0°C and 1 atm, but Sm³ (standard cubic meter) often uses 15°C or 20°C at 1 atm. The reference temperature depends on the industry, the company, and the manufacturer.

Osaka Gas's unit conversion table, for example, sets N at 0°C and S at 15°C. On that basis, 1 Nm³ = 1.055 Sm³ (288.15 ÷ 273.15). A 15°C difference in the reference changes the number for the same gas by about 5%, and a 20°C difference by about 7%. Two values can both say "standard" and still use different conditions. To convert to Sm³, use the same formula with that reference temperature and pressure in place of 0°C and 101.325 kPa. If the reference includes humidity, the water vapor creates a further difference.

Japanese pneumatic catalogs often use a third basis, ANR. SMC defines ANR as air at 20°C, 100 kPa absolute, and 65% relative humidity, citing ISO 8778 and JIS B 8393, and writes it after the unit, as in L/min (ANR).

Compressor free air delivery is usually stated at inlet conditions, too. Anest Iwata, a Japanese compressor maker, uses 20°C, 0.1013 MPa, and 65% relative humidity as its inlet condition. In the same material, it multiplies a demand of 500 NL/min (0°C, dry) by a company factor of 1.079 and selects a compressor rated at 540 L/min or more.

US readers will meet SCFM (standard cubic feet per minute), which has the same problem. "Standard" may mean 60°F or 68°F, among other temperatures, and the pressure may be 14.696 psia (1 atm), 14.73 psia, or 1 bar. Some definitions also fix a humidity. As a calculated reference, 1 Nm³/h equals about 0.622 SCFM at 60°F and 14.696 psia, or about 0.632 SCFM at 68°F and 14.696 psia (dry, ideal gas). Confirm which definition your compressor or flowmeter vendor uses.

Figure 5: Common Reference States Compared

Each is called "standard" by someone, but the temperature, pressure, and humidity all differ.

Nm³ (normal)0°C / 101.325 kPa / dry. Combustion air, fuel gas heating value, flue gas limits, blower ratings

Sm³ (standard)Often 15°C or 20°C / 1 atm. Defined by each company or industry (e.g., Osaka Gas uses 15°C for S)

ANR (pneumatic equipment)20°C / 100 kPa absolute / 65% RH. Written after the unit, as in L/min (ANR)

Compressor inlet conditionse.g., 20°C / 0.1013 MPa / 65%, as stated by the maker. Basis of catalog free air delivery

Japanese city gas meter (low pressure)15°C / 103.325 kPa (2 kPa gauge). The m³ on the gas bill is measured at this state

Actual conditionsLocal temperature and pressure. Pipe and duct velocity, tank and cylinder internal volume

ANR from SMC, inlet conditions from Anest Iwata, S from Osaka Gas, gas meters from J-Net21 (Organization for Small & Medium Enterprises and Regional Innovation, Japan). The same name can carry different conditions in different documents.

When you compare catalog or datasheet values, confirm which reference each number uses. Look for "(ANR)" after the unit, an N or S prefix or suffix, and a temperature in the notes. For duct velocity, always convert to actual volume first.

When to Use Nm3 and When to Use m3

When you design or select ducts, fans, or air compressors, the choice is not always obvious. The rule: use m³ when you need volume, and Nm³ when you need the amount (mass) of gas.

Air velocity in a duct, for example, depends on the actual temperature and pressure of the air passing through it, so you calculate it in m³. Combustion is different. The oxygen a burner needs depends on the amount of air, not its volume, so combustion air is calculated in Nm³, and so is the flue gas it produces.

Figure 6: Where m³ Applies and Where Nm³ Applies

Even for the same air, size equipment in m³ and count gas in Nm³.

Compressor free air delivery is often stated at the maker's inlet conditions (20°C, 65% RH, etc.), which differ from Nm³ by a few percent.

For the same reason, commercial and regulatory figures in Japan are usually on an Nm³ basis. City gas heating values are given per 1 m³ of gas at 0°C and 101.325 kPa, and Japan's soot, dust, and NOx emission standards are per 1 m³ of flue gas converted to 0°C and 1 atm.

Worked Examples: Combustion Air, Flue Gas, and City Gas

The same steps apply beyond compressed air. Near atmospheric pressure, you can treat the gauge pressure as zero and correct for temperature only.

Combustion Air at 30°C

A boiler burner needs 1,000 Nm³/h of air, and the forced-draft fan draws in air at 30°C (86°F). The volume the fan actually moves is:

Compared with 0°C, the fan must move about 11% more volume for the same Nm³. That is why the load on the fan changes between summer and winter as the intake temperature changes.

Flue Gas at 200°C

Now 1,000 Nm³/h of flue gas flows through the flue at 200°C (392°F):

Hot flue gas takes up about 1.7 times its normal volume, so size flues and ducts on the actual m³/h.

Figure 7: What 1,000 Nm³/h Becomes in Actual m³/h

Same amount of gas, but compressed air and hot flue gas differ in actual volume by more than ten times.

0.7 MPaG, 20°C (compressed air)~136 m³/h

1 atm, 0°C (normal state)1,000 m³/h

1 atm, 30°C (combustion air)~1,110 m³/h

1 atm, 200°C (flue gas)~1,732 m³/h

Ideal-gas values. The 0.7 MPaG, 20°C value uses the chart factor 0.136.

Japanese City Gas Meter Readings

If you review energy data from a plant in Japan, note that the m³ on a Japanese city gas bill is the volume that passed through the gas meter, not Nm³ at 0°C and 1 atm. According to J-Net21, a low-pressure gas meter reads volume at 15°C and 103.325 kPa (2 kPa gauge), and a medium-pressure meter reads volume at 15°C and 102.306 kPa. The factors to convert to Nm³ are therefore 0.9667 for low-pressure meters and 0.9571 for medium-pressure meters. The J-Net21 explanation assumes Tokyo Gas's heating value definition, so for other gas utilities, check the meter conditions in the utility's own documents.

These factors match the conversion formula. For a low-pressure meter:

Suppose a low-pressure meter records 1,000 m³ in a month. The standard heating value of 13A city gas, 45 MJ, is per 1 m³ of gas at 0°C and 101.325 kPa (Tokyo Gas).

Multiplying the meter reading directly by 45 MJ gives 45,000 MJ, an overestimate of about 3%. To get heat input or energy intensity right, convert to Nm³ before you apply the heating value. Japanese reporting forms differ on whether they expect the raw meter reading or the converted value, so follow the notes on each form.

Figure 8: From a City Gas Meter Reading to Heat Input

Multiply the billed m³ by a factor to get Nm³, then by the standard heating value.

Meter reading m³Low pressure: volume at 15°C, 2 kPa gauge

× 0.9667Medium pressure (pressure-corrected): × 0.9571

Normal state Nm³Dry gas at 0°C, 101.325 kPa

× 45 MJ/Nm³Standard heating value of 13A. 1,000 m³ ≈ 43.5 GJ

Factors from J-Net21; heating value from Tokyo Gas. Heating values and meter conditions can differ by gas utility and contract, so check the utility's documents.

Checklist for Japanese Datasheets and Catalogs

Use this list when a Japanese datasheet, flowmeter, or catalog gives a gas or air flow:

• Datasheet: the flow unit (Nm³/h, m³/h, Sm³/h) and the operating temperature and pressure fields
• Pressure: gauge (MPaG, kPaG) or absolute (MPa abs)
• Flowmeter: the nameplate or manual says whether it is temperature- and pressure-compensated (reads Nm³/h) or uncompensated (reads actual flow)
• Pneumatic catalog: "(ANR)" after the unit, or a note such as "converted to inlet conditions"
• Compressor rating: the inlet temperature, pressure, and humidity behind the free air delivery figure
• Sm³ or SCFM: the reference temperature and pressure used
• Gas meter data: low-pressure or medium-pressure meter (pressure correction or not)

If the conditions are not written down, do not compare the numbers as they are; ask the issuer. A 2–7% difference can push a compressor or blower selection up or down one size. Fans, blowers, and compressors also work over different pressure ranges and state airflow in different ways.

Questions for the Japanese Supplier

• Is this flow stated in Nm³ (0°C, 101.325 kPa, dry) or on another basis, such as Sm³ or ANR? What temperature, pressure, and humidity does it use?
• Is the pressure on the datasheet gauge or absolute?
• What are the actual operating temperature and pressure at the inlet and outlet of the equipment?
• Does the flowmeter compensate for temperature and pressure? If so, what reference conditions does it use for the displayed flow?
• Is the compressor capacity free air delivery at inlet conditions? What inlet conditions?
• Can you give the same flow in actual m³/h at the design conditions, or in SCFM at our reference?

A short inquiry you can adapt:

Subject: Flow basis for [equipment tag] datasheet

Your datasheet lists the combustion air flow as 1,000 Nm³/h and the supply pressure as 0.7 MPa. Please confirm (1) the reference conditions for Nm³ (temperature, pressure, and whether dry or humid), (2) whether 0.7 MPa is gauge or absolute pressure, and (3) the actual inlet temperature and pressure at the design point. If possible, please also give the flow in actual m³/h at those conditions.

Limits of This Guide

• The formula and chart treat the gas as ideal and dry. Humidity, high pressure, and gases close to condensing need corrections (see the FAQ).
• Reference conditions for Sm³, ANR, compressor ratings, and SCFM vary by company, industry, and document. The examples here come from the sources listed below; always use the definition on your own datasheet.
• The SCFM factors are our own calculations at the stated conditions, not values from a standard.
• The city gas factors and heating value are J-Net21 and Tokyo Gas values. Other utilities and contracts can differ.
• Equipment sizing and emission compliance follow the project specification and the applicable codes. This guide only explains the unit conversion.

FAQ

How Do You Convert Nm3/h to m3/h?

Use the same formula as for volume: multiply by (273.15 + T) / 273.15 and by 101.325 / (101.325 + P), with T in °C and P in kPa gauge. At 0.5 MPaG and 20°C, m³/h = Nm³/h × 0.181, and Nm³/h = m³/h × 5.53. For other conditions, use the chart above.

What Is the Difference Between Nm3 and Sm3?

The reference temperature. Nm³ is at 0°C and 1 atm; Sm³ is often at 15°C or 20°C, depending on the company or industry. With S at 15°C, 1 Nm³ = 1.055 Sm³. To convert to Sm³ or ANR, replace 273.15 and 101.325 in the formula with the absolute temperature and absolute pressure of that reference.

How Do You Convert Nm3 to kg?

Multiply the molecular weight of the gas (g/mol) by 44.6. That gives the mass in grams per Nm³, because 1 Nm³ is about 44.6 mol. For dry air (average molecular weight 28.97), that is about 1.29 kg/Nm³, so 100 Nm³/h of air is about 129 kg/h. For humid air or other gases, recalculate with their molecular weight.

What Is the Difference Between NL/min and L/min (ANR)?

NL/min is flow at 0°C and 1 atm on a dry basis. L/min (ANR) is flow at 20°C, 100 kPa, and 65% RH. Using the saturation vapor pressure of water at 20°C (about 2.34 kPa, NIST), we estimate that 1 m³ (ANR) contains about 0.91 Nm³ of dry air. So for the same air, the ANR number is about 10% larger. Makers treat humidity differently (Anest Iwata's compressor selection uses a factor of 1.079, for example), so follow the catalog notes when selecting equipment.

Does the Conversion Formula Work at High Pressure?

Yes, for typical plant compressed air up to about 1 MPa. The formula assumes an ideal gas. Using NIST data, the compressibility factor Z of nitrogen at 20°C and 0.7 MPa absolute is 0.9984, within 0.2% of an ideal gas. For gases at much higher pressure, or gases that liquefy easily such as propane, correct with the compressibility factor Z.

Sources

• Molar volume of an ideal gas at 0°C and 101.325 kPa: NIST, "Molar volume of ideal gas (273.15 K, 101.325 kPa)" (CODATA 2022)
• Stating conditions on the quantity rather than the unit: NIST SP 811, Guide for the Use of the SI, Chapter 7 (7.4, 7.5)
• Flue gas volume converted to 0°C and 1 atm in Japanese emission rules: e-Gov, Enforcement Regulations of the Air Pollution Control Act, Articles 4 and 5 (Japanese)
• Standard heating value of 13A and its reference state: Tokyo Gas, "Types, heating values, pressures, and components of city gas" (Japanese)
• Gas meter conditions and conversion factors to the normal state: J-Net21 (SMRJ), Q&A on differences in city gas heat totals (Japanese)
• City gas use converted to the normal state: Tokyo Gas FAQ, crude oil equivalent of city gas use (Japanese)
• m³(N) at 0°C and m³(S) at 15°C: Osaka Gas, Annual Report 2013, unit conversion table
• ANR (20°C, 100 kPa, 65% RH; ISO 8778, JIS B 8393): SMC, Energy Saving Program Ver. 4.1, glossary (Japanese)
• Compressor free air delivery and conversion from the normal state: Anest Iwata, "Basics of compressed air" (Japanese)
• Range of SCFM reference conditions: Wikipedia, "Standard cubic feet per minute"
• Nitrogen density (compressibility factor) and saturation pressure of water: NIST Chemistry WebBook, Thermophysical Properties of Fluid Systems
• Mean molecular weight of air (28.97 g/mol): NASA, Earth Fact Sheet