GPM, CFM, SCFM and m³/h: A Practical Flow Rate Conversion Guide
Flow rate is one of those quantities where everyone uses a different unit and assumes you know which one they mean. A pump catalog quotes GPM, an HVAC drawing lists CFM, a compressed air spec gives SCFM and the European data sheet for the same equipment uses m³/h. They're all volumetric flow, but the conversions aren't obvious and SCFM hides a trap that catches engineers regularly. Here's the practical guide.
What are GPM, CFM, SCFM and m³/h?
All four measure volumetric flow rate - how much volume of fluid passes a point per unit of time. GPM is US gallons per minute, used for water, fuel and most liquid pumps in North America. CFM is cubic feet per minute, used for HVAC airflow, fans and blowers. SCFM is standard cubic feet per minute - same volumetric unit as CFM, but referenced to a fixed temperature and pressure (more on that below). m³/h is cubic meters per hour, the standard SI unit used in European pump and compressor specs. They're all interchangeable mathematically, but each industry has its own convention.
GPM to m³/h conversion chart
The base conversion is 1 GPM = 0.227 m³/h = 0.0631 L/s = 3.785 L/min. Multiply GPM by 0.227 to get m³/h. Multiply by 0.0631 to get L/s. For quick reference at common pump sizes:
| GPM | m³/h | L/s | L/min |
|---|---|---|---|
| 1 | 0.227 | 0.063 | 3.79 |
| 10 | 2.27 | 0.631 | 37.9 |
| 50 | 11.4 | 3.16 | 189 |
| 100 | 22.7 | 6.31 | 379 |
| 500 | 114 | 31.5 | 1893 |
| 1000 | 227 | 63.1 | 3785 |
For any value not on the chart, use our GPM converter.
What's the difference between SCFM and ACFM?
This is the trap. SCFM (standard CFM) measures gas flow as if it were at a reference condition - typically 14.7 psia and 68°F (some industries use 60°F or 0°C - always check). ACFM (actual CFM) measures the gas at the real temperature and pressure where it's flowing. The two diverge whenever the gas is compressed or heated. A compressor rated at 100 SCFM delivers 100 cubic feet per minute of air equivalent to standard atmospheric conditions, but the actual volume coming out at 100 psig is only about 12.5 ACFM, because the air is compressed roughly 8:1. For incompressible liquids (water, oil) the distinction doesn't exist - 1 GPM is always 1 GPM. For gases and compressed air, always check whether a flow spec is standard or actual before sizing piping or equipment.
How do I convert m³/h to L/s?
Divide by 3.6. 1 m³/h = 0.278 L/s. That's because 1 m³ is 1000 litres and 1 hour is 3600 seconds, so the ratio is 1000/3600 = 0.2778. To go the other way, multiply L/s by 3.6 to get m³/h. For cubic meters per second to m³/h, multiply by 3600. You can run any of these directly in our m³/h to L/s converter.
Which flow rate unit should I use?
Match the convention of whoever you're communicating with. Quick reference:
- HVAC and air handling: CFM (US) or m³/h (Europe)
- Compressed air and pneumatics: SCFM (always check vs ACFM)
- Water and process pumps (US): GPM
- Water and process pumps (rest of world): m³/h or L/s
- Lab and analytical flow: mL/min or L/min
- Hydraulics: GPM (US) or L/min (Europe)
- Pipeline and large-scale flow: m³/s or millions of gallons per day (MGD)
If you're translating a European pump curve into US units, the path is almost always m³/h → GPM (multiply by 4.403) or L/s → GPM (multiply by 15.85). If you're sizing a compressed air system from a European compressor spec given in m³/h, convert to SCFM using 1 m³/h ≈ 0.589 SCFM at standard atmospheric conditions, but verify the reference temperature and pressure your spec uses, because the conversion factor shifts slightly between ISO, ANSI and CAGI definitions of "standard."