cfm, psi and bar conversion and selection guide

Identify the quantity before converting

Most confusion in compressor quotations comes from mixing two different quantities. Flow tells you how much air a compressor delivers per minute. Pressure tells you how hard that air pushes. A question such as “how many psi is 185 cfm?” has no answer, because one is a flow and the other a pressure. A 185 cfm machine might be built for 7 bar (101.5 psig) or for 10 bar (145 psig).

Flow conversion factors

• 1 cfm = 28.317 l/min = 0.4719 l/s = 0.02832 m³/min = 1.699 m³/h
• 1 m³/min = 35.31 cfm = 1,000 l/min = 60 m³/h
• 1 l/s = 2.119 cfm = 0.06 m³/min
• 1 m³/h = 0.5886 cfm

Keep the time unit with the number. Writing “28.3 litres” when you mean “28.3 litres per minute” turns a flow into a volume and leads to wrong receiver and pipe calculations.

Quick flow table for common compressor sizes

Values are rounded. For a quotation or a contract, convert from the original figure, not from a rounded table value.

Pressure conversion factors

• 1 bar = 14.504 psi = 100 kPa = 0.1 MPa
• 1 psi = 0.06895 bar = 6.895 kPa
• 1 kg/cm² = 0.981 bar = 14.22 psi
• 1 standard atmosphere = 1.013 bar = 14.696 psi

Is 7 bar exactly 100 psi? No. 7 bar is 101.5 psi. The two are used loosely as equivalents on site, which is fine for conversation but not for settings, test pressures or safety valve ratings.

Gauge and absolute pressure are not the same

A gauge on a compressor reads pressure above the surrounding atmosphere: bar(g) or psig. Absolute pressure adds atmospheric pressure: bar(a) or psia. At sea level, 7 bar(g) is about 8 bar(a). The difference matters in three places:

• Pressure ratios: compression ratio and stage design use absolute pressures.
• Gas laws and receiver calculations: always use absolute pressure.
• Altitude: atmospheric pressure falls with height, so the same gauge reading means a different absolute pressure on a high site.

Write the “g” or “a” every time. Our pressure unit and gauge-absolute conversion tool handles this step.

FAD, ACFM, SCFM and Nm³: read the label

A flow figure is only meaningful with its reference conditions.

Converting SCFM to m³/min with the simple factor changes only the units, not the reference conditions. To compare a standard figure with a FAD figure you must correct for temperature, pressure and humidity. See our FAD and reference condition conversion tool.

Worked example: keep the meaning through the conversion

A contractor has two quotations. One offers 12.7 m³/min FAD at 10 bar(g). The other offers 450 cfm at 150 psig. Converting: 12.7 × 35.31 = 448 cfm, and 10 bar is 145 psi. The machines look nearly identical. But the second quotation does not state whether 450 cfm is FAD or displacement. If it is displacement, its delivered air could be noticeably lower. The right step is to ask the supplier to confirm the basis and the test standard, not to pick the larger number.

Rounding can also mislead. A tool needing 5.0 m³/min, converted to 177 cfm and then rounded up to “a 185 cfm machine”, may leave no margin for hose losses, wear and a second tool. Size from the real demand plus a stated allowance.

Why higher pressure does not mean more flow

Raising the discharge pressure of a given compressor does not increase its flow; it usually reduces it and raises power use. As a rule of thumb, each extra bar costs about 7% more power. You cannot convert a pressure increase into extra output, and you cannot “convert” a 7 bar machine into a 10 bar machine by changing a setting if it is not designed for that pressure. Select the pressure the work needs at the point of use, plus line losses, and no more.

Volume, flow and storage are separate

A receiver is sized in litres or m³, not cfm. Storage helps smooth peaks, but it does not create air: over a full cycle the compressor must still deliver the average demand. To estimate how long a receiver can supply a short peak, use the volume, the allowable pressure drop and absolute pressures. Our receiver transient storage calculator explains the method.

Selecting a compressor once the units are clear

1. List each air user with its flow and minimum working pressure, in one unit system.
2. Apply a realistic usage factor for tools that do not run all the time.
3. Add allowances for leaks, hose and pipe losses, and future demand.
4. Set the compressor pressure at the highest user’s need plus distribution losses.
5. Compare machines on FAD at that pressure, from the same test standard.
6. Check site conditions: high ambient, altitude and dust reduce margin.

Other units you will meet on Indian sites

Older gauges, imported datasheets and local practice still use several other units. The ones that cause the most confusion are:

• kg/cm²: common on older Indian gauges and pressure vessels. It is close to bar but not equal: 7 kg/cm² is about 6.9 bar or 99.6 psi.
• kPa and MPa: used in standards and many engineering drawings. 700 kPa is 7 bar; 1 MPa is 10 bar or 145 psi.
• Imperial and US gallons: appear on imported receiver data. A US gallon is about 3.785 litres and an imperial gallon about 4.546 litres, so always check which one is meant.
• hp and kW: 1 kW is about 1.34 hp. Motor power is not the same as the compressor’s shaft power or the power drawn from the supply, so state which figure you are quoting.
• Specific power: kW per m³/min of FAD at a stated pressure, the fairest single figure for comparing the efficiency of electric compressors.

When a quotation mixes units, convert every figure to one system before comparing, and keep a note of the original value and its reference conditions beside each converted number. That simple record prevents most disputes about whether a machine delivered what was offered.

How Reddy Compressors helps

We sell new and used compressors, rent from our own fleet of 50–2,000 cfm and 2–30 bar machines, and service and supply parts for ELGi, Atlas Copco, Ingersoll Rand, KAESER, Chicago Pneumatic and other brands as an independent multi-brand specialist, not an authorised dealer. We have tie-ups with all major and reputed brands. If two quotations use different units or reference conditions, send them to us and we will put them on the same basis and explain what each one actually offers. Our teams cover Telangana and Andhra Pradesh, and we supply across India from Srinilayam, 12-13-200, First Floor, Street No. 1, Tarnaka, Secunderabad 500017. Phone +91 99590 60718 or +91 92468 88812.

What to send us

• The figures you need converted, exactly as written, with units.
• Quotation or datasheet pages showing the flow basis (FAD, displacement or standard).
• Your tools or process users with their air consumption and pressure.
• Site altitude and typical summer ambient temperature.

Frequently asked questions

How many psi is 185 cfm?

There is no conversion, because cfm is flow and psi is pressure. A 185 cfm compressor is usually built for about 7 bar (101.5 psig), and some versions run at 10 bar (145 psig). Check the nameplate or datasheet for the rated working pressure. 185 cfm on its own converts to about 5.2 m³/min or 87 litres per second.

Is 1 cfm equal to 28.3 litres per minute?

Yes. One cubic foot per minute is 28.317 litres per minute, usually rounded to 28.3. That is also 0.0283 m³/min or 0.472 litres per second. Remember the “per minute”: 28.3 litres on its own is a volume, not a flow, and mixing the two causes errors in receiver and pipe sizing.

Is 7 bar the same as 100 psi?

Nearly, but not exactly. 7 bar is 101.5 psi, and 100 psi is 6.9 bar. Site users treat them as equal, which is acceptable in conversation. For pressure switch settings, safety valve ratings, test pressures and quotations, use the precise figure and state whether the pressure is gauge or absolute.

How do I convert SCFM to m³/min?

Multiply by 0.0283 to change the units. That keeps the original standard reference conditions, so the result is “standard” m³/min, not FAD. To compare it with a compressor’s FAD you must correct for the temperature, pressure and humidity of each reference. Ask the supplier which standard their figure uses.

What is the difference between FAD and displacement?

Displacement is the swept volume of the compression element before any losses. FAD is the air actually delivered, restated at inlet conditions and normally measured to ISO 1217. FAD is always lower than displacement. When comparing compressors, compare FAD at the same working pressure from the same test standard.

Does a higher-pressure compressor give more air?

No. Pressure and flow are different quantities. Running a compressor at a higher pressure usually lowers its delivered flow and raises power use, roughly 7% more power for each extra bar. Choose the pressure your work needs at the point of use, plus losses, and then select for the flow required at that pressure.

Related pages

• Pressure unit and gauge-absolute conversion tool
• FAD and reference condition conversion tool
• Compressed air demand calculator
• 185–250 cfm compressors
• Portable compressors
• Compressor rental