Flow Rate Calculator
Flow rate from a volume and a time, or from a velocity through a pipe bore.
What is Flow Rate?
Flow rate is volume per unit time, and there are two honest ways to arrive at it: measure a volume against a stopwatch, or multiply a velocity by the area it passes through. The first needs no assumptions but averages out pulsation; the second is what pipe sizing works in, and it needs the velocity to be a mean across the section. Both are here because the two answers should agree, and when they do not the pipe is not delivering what the sizing assumed.
How it works
In volume-and-time mode, litres are converted to cubic metres and divided by the seconds. In velocity-and-area mode, π × (d ÷ 2)² gives the internal area, which multiplies the velocity. Either way the flow is printed in litres per second, litres per minute, cubic metres per hour and US gallons per minute, because a pump rated in GPM and a requirement written in L/min differ by a factor of nearly four — 1 L/s is 15.85 GPM.
- Enter your input. Type or paste your input into the field above — the tool responds instantly.
- Review the result. Output updates live as you type. Everything runs entirely in your browser.
- Copy or download. Use the Copy button to grab the result, or Download to save it as a file.
Examples
Realistic sample
Type or paste any realistic input — the tool computes the result locally and instantly.
Common mistakes
Expecting a server round-trip
Nothing is uploaded — every tool in this category runs entirely in your browser.