Understanding volumetric flow
Volumetric flow is simply how much volume passes a point per unit time: river discharge, pump output, or the reading on a rotameter. This page converts between dozens of rate units by normalizing everything to cubic meters per second. The gasoline rows are a special case: they treat mass flow as volume flow using a fixed density for gasoline near room temperature, which is how many legacy tables stay consistent from sheet to sheet.
How volumetric flow conversion works
Pick a rate unit. Internally we ask: how many cubic meters per second does one unit of that rate represent? You multiply your number by the source factor, then divide by the target factor. Same pattern as converting inches to feet, except the “thing” in the numerator is volume per time, not length.
Result = Value × (source in m³/s per unit) ÷ (target in m³/s per unit)
Example: 500 US gallons per minute to liters per second. One US gallon is 0.00378541 m³, so one gallon per minute is that volume divided by 60 seconds. Chain that into liters (multiply m³ by 1000) and you get the familiar ballpark people check by hand when a pump spec sheet uses different units than the pipe schedule.
Conversion factors: units worth knowing
The dropdown lists every factor we use. Below are the ones that tend to trip people up in real projects.
Cubic meter per second [m³/s]
Factor: 1 (base)
SI-friendly and common in large civil works and big pumps. River discharge and cooling water specs often land here or in liters per second.
Liter per second [L/s]
Factor: 0.001 m³/s per L/s
One liter is exactly one cubic decimeter, so the jump to m³ is a decimal shift. Plumbing and small pump curves use L/s or L/min constantly.
US gallon per minute
Factor: US gallon volume ÷ 60 s
The US gallon is defined as 231 cubic inches. If someone says “GPM” without a country, in American contexts they almost always mean US liquid gallons.
UK gallon per minute
Factor: imperial gallon volume ÷ 60 s
The imperial gallon is larger than the US gallon. Mixing the two on a bid is expensive, so we label both explicitly.
Barrel (US) per day
Factor: 42 US gal per barrel, spread over a day
Oilfield shorthand. A “barrel” in this row is the 42-gallon petroleum barrel, not a random drum size from a warehouse.
Acre-foot per year
Factor: volume of one acre-foot per Julian-style year
Water rights and irrigation math love acre-feet per year. The year length here follows the same convention used in standard conversion tables so numbers match what people already trust.
Cubic foot per minute (CFM)
Factor: one cubic foot per minute to m³/s
HVAC fans, dust collection, and shop compressors love CFM. One cubic foot is exactly 28.316846592 liters by definition.
Gasoline rows (15.5 °C)
Factor: fixed density, not a separate fluid model
Those lines convert pounds or kilograms per time into volume rate by assuming a single density for gasoline at about 15.5 °C. They are handy for reconciling tank tickets and mass meters, not for cryogenic precision.
Common volumetric flow conversions at a glance
Round numbers you can sanity-check before you trust a spreadsheet.
| From | To | Rule of thumb | Example |
|---|---|---|---|
| L/s | L/min | × 60 | 2 L/s = 120 L/min |
| US gpm | L/min | × 3.78541 | 50 gpm ≈ 189 L/min |
| m³/h | L/s | ÷ 3.6 | 18 m³/h = 5 L/s |
| ft³/s | L/s | × 28.31685 | 2 cfs ≈ 56.6 L/s |
| m³/d | L/min | × 1000 ÷ 1440 | 1 m³/d ≈ 0.694 L/min |
| lb/s gasoline | US gpm | use fixed density row | Use the tool; density is baked in |
Minutes, hours, and days under the hood
Almost all confusion comes from forgetting that the word “per minute” sits in the denominator twice when you combine mental math with volume. If you convert cubic meters per hour to liters per second, you are folding in both the volume ratio (1000 L per m³) and the time ratio (3600 seconds per hour). Doing it in two explicit steps on paper still beats trusting memory when the bid is due at five.
When something looks “too big” or “too small,” flip the units and check whether you accidentally inverted a day versus a second. That single mistake moves answers by factors of tens of thousands.
Volumetric flow FAQ
Is a UK gallon the same as a US gallon?
No. The imperial (UK) gallon is larger. Always match the gallon label on your instrument to the gallon label in the calculator, especially on imported pump curves.
Why are there gasoline pounds per second?
Some custody transfer systems measure mass directly. Those rows translate mass rate into volume rate using one fixed gasoline density so you can compare against a turbine meter quoted in gallons.
What does CFM stand for?
Cubic feet per minute. It is volume rate, not “compressed air power.” Pair it with pressure and temperature when you move into mass or energy.
How many liters per second is one cubic meter per second?
Exactly one thousand. A cubic meter is one thousand liters by definition, so the rate scales the same way.