How does the pipe velocity calculator work?

It converts your flow rate from litres per minute to cubic metres per second by dividing by 60,000, works out the pipe cross-section area from the internal diameter using pi times diameter squared divided by four, and then divides flow by area to get velocity. The result is shown in metres per second and feet per second, so you can see how fast water actually moves inside the pipe.

What inputs do I need to enter?

Just two numbers. First, the flow rate in litres per minute through that pipe run, which comes from your fixture demand or pump duty. Second, the pipe internal diameter in millimetres, meaning the bore, not the nominal or outside size. Bore is smaller than the outside diameter and varies by material and pressure class, so check the pipe manufacturer's dimension table for the true internal figure.

What is a safe water velocity in a supply pipe?

For domestic supply pipework a velocity of roughly 1 to 1.5 metres per second is comfortable, quiet and efficient. Up to about 2.4 metres per second is generally acceptable, and this tool flags anything above that as high because fast water causes flow noise, water hammer on valve closure and gradual erosion of pipe walls. These are typical planning figures, so verify limits against NBC 2016 Part 9 and the pipe manufacturer's data.

Interactive Calculator · 2026

Pipe Velocity Calculator

Find the water velocity inside a pipe from the flow rate and the internal diameter. Enter the flow and the pipe bore — get the velocity in m/s and ft/s, and an instant flag if it runs high enough to cause noise, water hammer or erosion.

Water velocity (30 L/min through 25 mm bore)0.00 m/s≈ 0.00 ft/s · status: Ideal

Measured velocity vs the ~2.4 m/s advisory limit for supply pipework

Your pipe run

Flow rate (L/min)

Volume of water passing through the pipe per minute.

Pipe internal diameter (mm)

Bore, not the nominal size — internal diameter is smaller than the outside diameter.

Ideal

1–1.5 m/s — ideal band for supply pipework: quiet, efficient and low wear.

Velocity

0.00 m/s

Velocity

0.00 ft/s

Status

Velocity vs the advisory limit

Keep supply velocity under about 2.4 m/s to avoid noise, water hammer and erosion.

Your run carries water at 1.02 m/s against a ~2.4 m/s advisory ceiling. That sits within the advisory band, so noise, water hammer and erosion stay in check.

To drop velocity, step up one pipe size — velocity falls with the square of the bore.

How this is calculated

Flow in m³/s = flow ÷ 60,000 = 30 ÷ 60,000 = 0.000500 m³/s.
Pipe area = π × (diameter ÷ 1000)² ÷ 4 = π × (25 ÷ 1000)² ÷ 4 = 0.000491 m².
Velocity = flow ÷ area = 0.000500 ÷ 0.000491 = 1.02 m/s (3.34 ft/s).

Indicative for concept planning. The ~2.4 m/s ceiling is a typical advisory figure — high velocity causes noise, water hammer and erosion. Verify limits against NBC 2016 Part 9 and the pipe manufacturer's data, and confirm with a qualified consultant before procurement.

Understand the number you just got

Plumbing Pipes Guide (India)Pipe materials, sizes and where each type belongs in a building.Noisy Pipes & Water Hammer (India)Why high velocity makes pipes bang, and how to fix it.

Frequently asked questions

How does the pipe velocity calculator work?: It converts your flow rate from litres per minute to cubic metres per second by dividing by 60,000, works out the pipe cross-section area from the internal diameter using pi times diameter squared divided by four, and then divides flow by area to get velocity. The result is shown in metres per second and feet per second, so you can see how fast water actually moves inside the pipe.
What inputs do I need to enter?: Just two numbers. First, the flow rate in litres per minute through that pipe run, which comes from your fixture demand or pump duty. Second, the pipe internal diameter in millimetres, meaning the bore, not the nominal or outside size. Bore is smaller than the outside diameter and varies by material and pressure class, so check the pipe manufacturer's dimension table for the true internal figure.
What is a safe water velocity in a supply pipe?: For domestic supply pipework a velocity of roughly 1 to 1.5 metres per second is comfortable, quiet and efficient. Up to about 2.4 metres per second is generally acceptable, and this tool flags anything above that as high because fast water causes flow noise, water hammer on valve closure and gradual erosion of pipe walls. These are typical planning figures, so verify limits against NBC 2016 Part 9 and the pipe manufacturer's data.

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