lb/hr to SCFM Converter
A gas given in pounds an hour can be turned into standard cubic feet a minute. You only need its molar mass.
Quick answer: multiply the lb/hr by 385.32, then divide by 60 times the molar mass. For example, 100 lb/hr, 28.96 g/mol is 22.175 SCFM, 100 lb/hr, 44.01 g/mol is 14.592 SCFM and 1,000 lb/hr, 28.01 g/mol is 229.28 SCFM.
The lb/hr to SCFM formula
SCFM is a molar flow expressed as a volume at standard conditions (Wikipedia: Standard cubic feet per minute).
One pound-mole of gas fills 385.32 ft³ at 68 °F and 14.696 psia, so SCFM equals lb/hr × 385.32, divided by 60 times the molar mass.
Take 100 lb/hr, 28.96 g/mol. 100 × 385.32 ÷ (60 × 28.96) gives 22.175 SCFM.
Take 100 lb/hr, 44.01 g/mol. 100 × 385.32 ÷ (60 × 44.01) gives 14.592 SCFM.
Mass to standard volume
A standard cubic foot is a fixed amount of gas, set by temperature and pressure (Wikipedia: Standard cubic feet per minute).
Standard conditions differ, so always state them (Wikipedia: Standard cubic feet per minute).
This tool uses 68 °F and 14.696 psia.
How to convert lb/hr to SCFM step by step
- Write down the mass flow in lb/hr.
- Write down the molar mass of the gas in g/mol.
- Multiply lb/hr by 385.32, and divide by 60 times the molar mass.
- The answer is in SCFM.
Example 1: 100 lb/hr, 28.96 g/mol
- Start with 100 lb/hr, 28.96 g/mol.
- 100 × 385.32 ÷ (60 × 28.96) = 22.175.
- The flow is 22.175 SCFM.
100 lb/hr, 28.96 g/mol = 22.175 SCFM
Example 2: 100 lb/hr, 44.01 g/mol
- Start with 100 lb/hr, 44.01 g/mol.
- 100 × 385.32 ÷ (60 × 44.01) = 14.592.
- The flow is 14.592 SCFM.
100 lb/hr, 44.01 g/mol = 14.592 SCFM
Example 3: 1,000 lb/hr, 28.01 g/mol
- Start with 1,000 lb/hr, 28.01 g/mol.
- 1,000 × 385.32 ÷ (60 × 28.01) = 229.28.
- The flow is 229.28 SCFM.
1,000 lb/hr, 28.01 g/mol = 229.28 SCFM
Wikipedia gives 1,000 kg/h of air as 481 SCFM at 60 °F. At 68 °F, as here, the answer is about 489 SCFM (Wikipedia: Standard cubic feet per minute).
lb/hr to SCFM conversion table
| Mass flow and gas | Flow (SCFM) | Flow (SLPM) |
|---|---|---|
| 100 lb/hr, 28.96 g/mol | 22.175 SCFM | 627.94 SLPM |
| 100 lb/hr, 44.01 g/mol | 14.592 SCFM | 413.2 SLPM |
| 100 lb/hr, 28.01 g/mol | 22.928 SCFM | 649.24 SLPM |
| 100 lb/hr, 32 g/mol | 20.069 SCFM | 568.28 SLPM |
| 500 lb/hr, 28.96 g/mol | 110.88 SCFM | 3,139.69 SLPM |
| 1,000 lb/hr, 28.01 g/mol | 229.28 SCFM | 6,492.35 SLPM |
| 250 lb/hr, 44.01 g/mol | 36.48 SCFM | 1,033.01 SLPM |
| 60 lb/hr, 32 g/mol | 12.041 SCFM | 340.97 SLPM |
The highlighted row is the default of the calculator. The last column gives SLPM.
A quick mental shortcut for lb/hr to SCFM
For air, divide lb/hr by 4.5. So 100 lb/hr is about 22 SCFM.
Use a different divisor for other gases.
What SCFM measures
SCFM is the flow of gas at standard conditions. It counts the amount of gas, not the space it takes.
That is why it is used for gas flows.
What molar mass is
Molar mass is the mass of one mole of gas, in g/mol. Air is about 28.96, nitrogen 28.01, oxygen 32.00 and CO2 44.01.
A heavier gas gives fewer cubic feet for the same pounds.
Where 385.32 comes from
It is the volume of one lb-mole of gas at 68 °F and 14.696 psia, in cubic feet.
That volume is the same for all ideal gases.
Standard conditions differ
Standards use 0, 15, 20 or 25 °C and different pressures (Wikipedia: Standard cubic feet per minute).
At 60 °F the factor is about 379.5.
An air example
A line of 100 lb/hr of air is 22.18 SCFM.
In SLPM that is 628.
A CO2 example
A line of 100 lb/hr of CO2 is 14.59 SCFM.
CO2 is heavier, so it fills less volume.
Going the other way
To find lb/hr from SCFM, multiply by 60 and the molar mass, then divide by 385.32.
So 22.18 SCFM of air is 100 lb/hr.
Real gases
The sum assumes an ideal gas. Real gases at high pressure need a correction (Wikipedia: Standard cubic feet per minute).
For low pressures the error is small.
Check your answer
A heavier gas should give a smaller SCFM for the same lb/hr.
Multiply back and you should get your lb/hr.
A worked example
100 lb/hr of nitrogen, with a molar mass of 28.01, is about 22.9 SCFM.
An air example
100 lb/hr of air, with a molar mass of 28.97, is about 22.2 SCFM. Use the molar mass of your own gas.
Quick conversion answers
| Conversion | Result |
|---|---|
| 60 lb/hr, 32 g/mol | 12.041 SCFM |
| 100 lb/hr, 28.96 g/mol | 22.175 SCFM |
| 100 lb/hr, 44.01 g/mol | 14.592 SCFM |
| 100 lb/hr, 28.01 g/mol | 22.928 SCFM |
| 250 lb/hr, 44.01 g/mol | 36.48 SCFM |
| 1,000 lb/hr, 28.01 g/mol | 229.28 SCFM |
Where this conversion is used
Plant staff convert gas flows.
Environmental staff compare emissions.
Students practise gas maths.
Common mistakes to avoid
- Using the wrong molar mass. Each gas has its own.
- Mixing standard conditions. State the temperature and pressure.
- Mixing minutes and hours. lb/hr is per hour.
- Rounding too early. The answer for 100 lb/hr, 44.01 g/mol is 14.592 SCFM. Cut it to 15 SCFM and you are off by about 2.8 percent, and the gap grows if you reuse it.
Related converters
A nitrogen line
A line of 1,000 lb/hr of nitrogen is 229.3 SCFM.
In SLPM that is 6,492.
An oxygen feed
A feed of 60 lb/hr of oxygen is 12.04 SCFM.
In SLPM that is 340.9.
Frequently asked questions
How do I convert lb/hr to SCFM?
Multiply lb/hr by 385.32, then divide by 60 times the molar mass.
How many SCFM is 100 lb/hr of air?
About 22.18 SCFM.
Why 385.32?
It is the cubic feet in one lb-mole at 68 °F and 14.696 psia.
What molar mass for air?
About 28.96 g/mol.
Do standard conditions matter?
Yes. A different standard changes the factor.
Does it work for any gas?
Yes, with the right molar mass, at low pressure.
Sources
- Wikipedia: Standard cubic feet per minute (en.wikipedia.org)
- Wikipedia: Mass flow rate (en.wikipedia.org)
