Water Flow Calculator
Calculate water flow through a pipe or outlet from its diameter and water velocity.
How it works
- 1Enter the inner diameter of the pipe or outlet (mm or in).
- 2Enter the water velocity — taps and hoses are typically 0.5–3 m/s.
- 3The calculator applies Q = (π/4·d²)·v and shows the flow in L/min.
Use cases
- Sizing a garden hose or irrigation line for adequate flow.
- Estimating how long it takes to fill a tank, pool, or container.
- Checking whether a supply line can feed a fixture or appliance.
Frequently asked questions
What formula does this use?
Q = (π/4·d²)·v. A 25 mm pipe at 1.5 m/s has an area of 0.000491 m² and flows about 0.000736 m³/s, or roughly 44 L/min.
What is a typical household water velocity?
Residential supply pipes run at 0.5–3 m/s. Above 3 m/s causes noise and erosion; below 0.5 m/s lets sediment settle.
How accurate is the result?
It assumes full-bore, uniform velocity with no friction. Real flow is a little lower due to roughness and fittings — use it as a planning estimate.
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