Calculate gas flow rate in CFH from gas volume and time, or estimate how long a tank or cylinder will last at a given gas flow rate.
- All Unit Converters
- CFM to Static Pressure Calculator
- LB/HR to SCFM Calculator
- SLPM to SCFH Calculator
CFH Formula
CFH stands for cubic feet per hour. The calculator runs one of two formulas depending on the tab you pick.
Flow rate mode:
CFH = V / T
- CFH = flow rate in cubic feet per hour (ft³/hr)
- V = gas volume used, converted to cubic feet
- T = elapsed time, converted to hours
Tank duration mode:
T = V / CFH
- T = run time in hours
- V = tank or cylinder volume in cubic feet
- CFH = flow rate in cubic feet per hour
Both formulas assume the gas volume is measured at the same reference conditions as the flow rate (typically standard temperature and pressure for compressed gas cylinders rated in SCF). The calculator handles unit conversion using 1 m³ = 35.3147 ft³ and 1 ft³ = 28.3168 L.
Typical CFH Values and Tank Run Times
Use these as sanity checks against your calculator output.
| Application | Typical CFH |
|---|---|
| MIG welding (argon/CO₂ mix) | 15–25 |
| TIG welding (argon) | 15–20 |
| Gas water heater | 35–45 |
| Gas range (all burners) | 60–80 |
| Residential furnace | 100–250 |
| Commercial boiler | 400+ |
| Cylinder size | At 15 CFH | At 20 CFH | At 30 CFH |
|---|---|---|---|
| 40 ft³ | 2.7 hr | 2.0 hr | 1.3 hr |
| 80 ft³ | 5.3 hr | 4.0 hr | 2.7 hr |
| 125 ft³ | 8.3 hr | 6.3 hr | 4.2 hr |
| 250 ft³ | 16.7 hr | 12.5 hr | 8.3 hr |
Example
You used 30 ft³ of argon over 90 minutes of welding. What is the flow rate in CFH?
Convert time: 90 min ÷ 60 = 1.5 hr.
Apply the formula: CFH = 30 ÷ 1.5 = 20 CFH.
That puts you in the normal MIG range. If your regulator was set to 20 CFH, the math checks out.
FAQ
Is CFH the same as SCFH? In practice for gas cylinders, yes. SCFH (standard cubic feet per hour) specifies that the volume is measured at standard temperature and pressure. Cylinder ratings and flowmeters use the same reference, so CFH and SCFH are used interchangeably.
How do I convert CFH to CFM? Divide by 60. 60 CFH equals 1 CFM.
Why does my tank empty faster than the calculator predicts? Real-world losses include gas wasted at start/stop, leaks at fittings, and purging lines. Plan on roughly 10–15% less usable run time than the math gives you.
