Flow Converter

Flow Rate Converter

Convert between liters per minute, liters per second, cubic meters per hour, gallons per minute (US), gallons per hour, and cubic feet per minute (CFM). Flow rate conversions come up constantly in plumbing design, HVAC commissioning, chemical processing, irrigation planning, and fire suppression engineering — and getting the wrong unit can mean undersized pipes, overloaded pumps, or failed inspections.

How Flow Rate Conversion Works

All conversions use liters per minute (L/min) as the internal base unit. The formula is:

result = input x (source factor in L/min) / (target factor in L/min)

Key factors:

• 1 US gal/min = 3.78541 L/min
• 1 Imperial gal/min = 4.54609 L/min
• 1 CFM (ft3/min) = 28.3168 L/min
• 1 m3/h = 16.6667 L/min
• 1 L/s = 60 L/min

Worked Examples

Example 1 — Residential water meter (GPM to L/min) A household meter reads 8 GPM during peak use. 8 x 3.78541 = 30.28 L/min

Example 2 — HVAC supply air (CFM to m3/h) A residential air handler is rated at 1,200 CFM. 1,200 x 28.3168 / 16.6667 = 2,037.6 m3/h

Example 3 — Chemical dosing pump (L/h to L/min) A dosing pump is rated at 480 L/h. 480 / 60 = 8.0 L/min

Flow Rate Reference Table

When to Use a Flow Converter

• Comparing US equipment specs (GPM) against European datasheets (m3/h or L/min)
• Sizing a pump when the manufacturer curve is in GPM but your system is designed in L/min
• Converting HVAC airflow from CFM to m3/h for international equipment or reports
• Matching irrigation system output (GPH) to plant water requirement data (L/h)
• Verifying fire sprinkler density requirements where codes mix GPM and L/min values

Common Mistakes

1. Confusing US and Imperial gallons. A US gallon is 3.785 L; an Imperial gallon is 4.546 L — about 20% larger. Pump specs and plumbing codes in the UK and Canada use Imperial gallons, so always confirm the source before converting.
2. Forgetting to square root pipe area when estimating velocity. Flow rate alone does not tell you velocity — you also need the pipe’s cross-sectional area. Convert flow rate first, then apply Q = A x v.
3. Mixing L/s and L/min. Both units appear in plumbing literature. A value of 0.5 L/s looks small but equals 30 L/min — a meaningful difference when sizing fixtures.
4. Using CFM for liquid flow. CFM is a volume-per-time unit used almost exclusively for air and gas. Applying it to liquid flow calculations will give nonsensical results.

Quick Reference Benchmarks

Tips

• A US gallon is 3.785 L and an Imperial gallon is 4.546 L — when in doubt, ask the supplier which standard applies.
• For HVAC systems, 400 CFM per ton of cooling is the standard US rule of thumb; convert to m3/h (multiply by 1.699) when specifying international equipment.
• Liters per second is preferred in fire engineering and large civil applications; liters per minute is more common in medical and small plumbing contexts.
• When pump curves are published in GPM, convert your design flow to GPM before reading the curve — do not try to interpolate across unit systems.
• Cubic meters per hour (m3/h) is the dominant metric unit in industrial process engineering; keep system calculations consistent in that unit and convert only for final documentation.
• Always note the temperature when converting gas flows — gas volume changes with temperature and pressure, so standard conditions (0 C, 1 atm) must be specified alongside the flow rate.