# Pipe Flow Rate Calculator

URL: https://speedycalculator.com/calculators/physics/flow-rate/
Last updated: 2026-10-25

> The flow rate calculator finds the volumetric flow through a pipe from its inner diameter and the fluid velocity, Q = A × v, in litres per minute, gallons per minute and cubic metres per hour.

## Inputs

- Inner diameter (mm, in, cm, m)
- Fluid velocity (m/s, km/h, mph, ft/s, knots)

## Results

- Flow rate

## Formula

```
Q = π (d ÷ 2)² × v
```

## Explanation

Flow rate links pipe size and speed: the same flow through a smaller pipe must move faster.

### How to use the Pipe Flow Rate Calculator

- **Inner diameter**
- **Fluid velocity**
- Want to work backwards? Type a value into **Flow rate** and **Fluid velocity** is calculated for you.

Results update as you type, and every field accepts the units shown in its menu.

### How it works

Multiply the pipe’s cross-sectional area by the average velocity.

### Inputs explained

FieldWhat to enterInner diameterUnits: mm, in, cm, mFluid velocityUnits: m/s, km/h, mph, ft/s, knots

### Example values

How the main result changes when **Fluid velocity** changes and everything else stays at the example values above:

Fluid velocity (m/s)Flow rate (L/min)0.7522.091.1333.131.544.181.8855.222.2566.27388.36

## Worked example

Inputs — Inner diameter: 25 mm; Fluid velocity: 1.5 m/s.

Results — **Flow rate = 44.18 L/min**.

## FAQ

**What velocity is typical for water pipes?**
About 0.5–2.5 m/s in domestic plumbing.

**Why use inner diameter?**
Only the open bore carries fluid.

**What formula does the Pipe Flow Rate Calculator use?**
Q = π (d ÷ 2)² × v.

**Can I work backwards from the result?**
Yes. Type the result you want into Flow rate and the calculator finds the matching fluid velocity.