GPM, L/min, m³/h and CFM
- GPM (US gallons per minute): pumps, well pumps, showerheads and faucets. US federal law caps showerheads at 2.5 GPM at 80 psi (Energy Policy Act of 1992).
- L/min (LPM) and m³/h: the metric equivalents on European and Asian pump curves.
- CFM (cubic feet per minute): fans, HVAC airflow, compressors and dust collectors.
- UK gal/min: the imperial gallon (4.546 L) is 20% larger than the US gallon (3.785 L), so always check which one a spec uses.
1 US gal = 231 in³ = 3.785411784 L (exact) → 1 GPM = 3.785412 L/min = 0.227125 m³/h
1 UK gal = 4.54609 L (exact) → 1 UK gal/min = 4.54609 L/min
1 ft³ = 28.316846592 L → 1 CFM = 28.31685 L/min = 1.69901 m³/h
1 m³/h = 16.6667 L/min = 0.277778 L/s
GPM to L/min and m³/h chart
| GPM | L/min | m³/h | L/s |
|---|---|---|---|
| 0.5 GPM | 1.893 | 0.1136 | 0.03155 |
| 1 GPM | 3.785 | 0.2271 | 0.06309 |
| 1.5 GPM | 5.678 | 0.3407 | 0.09464 |
| 1.8 GPM | 6.814 | 0.4088 | 0.1136 |
| 2 GPM | 7.571 | 0.4542 | 0.1262 |
| 2.5 GPM | 9.464 | 0.5678 | 0.1577 |
| 5 GPM | 18.93 | 1.136 | 0.3155 |
| 10 GPM | 37.85 | 2.271 | 0.6309 |
| 20 GPM | 75.71 | 4.542 | 1.262 |
| 50 GPM | 189.3 | 11.36 | 3.155 |
| 100 GPM | 378.5 | 22.71 | 6.309 |
Worked example
A European pump rated at 3 m³/h: 3 × 1,000 ÷ 60 = 50 L/min = 13.21 GPM. A 2.5 GPM showerhead uses 2.5 × 3.785 = 9.464 L/min, so a 10-minute shower is about 95 L (25 gallons).
Frequently asked questions
How many L/min is 1 GPM?
1 US GPM = 3.785 L/min = 0.227 m³/h. One UK gallon per minute is 4.546 L/min.
How many GPM is 1 m³/h?
1 m³/h = 4.403 US GPM = 16.67 L/min.
How many m³/h is 1 CFM?
1 CFM = 1.699 m³/h = 28.32 L/min.