Pipe Flow Calculator
Flow rate through a pipe from velocity and bore — or the velocity a flow implies.
What is Pipe Flow?
Flow rate, mean velocity and pipe bore are three quantities with one relation between them: Q = V × A. Sizing a pipe is really choosing a velocity (fast enough to carry solids, slow enough not to erode or roar) and reading the bore that delivers the required flow at it. This page works the relation in both directions, which is what makes it useful when a pump's curve is quoted in one unit and the requirement in another.
How it works
The internal area is π × (d ÷ 2)², with d the bore — not the outside diameter and not the nominal size, both of which are larger. Multiplying by velocity gives the flow in m³/s, converted to litres per second, litres per minute, cubic metres per hour and US gallons per minute. Running it backwards divides the flow by the area. A 50 mm bore at 2 m/s moves 3.93 L/s, which is 236 L/min or 62 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.