Flow Rate

Volumetric flow rate measures how much fluid volume passes a point per unit of time. The SI unit is the cubic metre per second (m³/s), but practitioners almost never work at that scale. Plumbing uses litres per minute, irrigation uses litres per second or cubic metres per hour, and HVAC balances run on cubic feet per minute (CFM). The range between smallest and largest flow-rate unit in common use spans roughly 9 orders of magnitude.

A key trap in international work is the gallon. The US gallon equals 3.785411784 L while the UK (imperial) gallon equals 4.54609 L, so 1 UK gpm is about 1.20095 US gpm. Quietly mixing them distorts pump and piping specifications by roughly 20%. Imported industrial equipment specified in UK gallons but installed on a US water main will under-deliver against its nameplate rating every time.

Real-world reference points help ground abstract units. A modern efficient shower head flows around 9.5 L/min (2.5 US gpm). A kitchen faucet at full open delivers 6 to 8 L/min. A garden hose at full open delivers 40 to 60 L/min depending on diameter and supply pressure. HVAC engineers translate refrigeration tonnage to airflow: rooftop units often spec 400 CFM per ton of cooling capacity. Water treatment plants scale into thousands of m³/h.

Flow rate conversions matter most in pump selection and duct sizing. Pump curves show head (pressure) against flow rate; pick the wrong unit axis and you commit to a pump that delivers the right head at the wrong flow, or vice versa. Cooling tower manufacturers specify duty in kW or tons of refrigeration, both of which require an airflow CFM figure to size fans and plenums.

This converter supports 12 flow-rate units covering m³, L, mL in SI form, US and UK gallons in customary form, and ft³ in imperial form, with per-second, per-minute, and per-hour denominators. The exact factors (1 US gal = 3.785411784 L, 1 UK gal = 4.54609 L, 1 ft³ = 0.028316846592 m³) come from NIST Handbook 44 and the UK Weights and Measures Act.