Pipe Size From Flow Velocity Calculator
Find the pipe inside diameter needed to carry a given flow rate at a target velocity, using A = Q/V. Shows the required diameter in mm and inches and the actual velocity in each standard Schedule 40 pipe size, so you can pick the nearest size at a glance.
Input
Typical water lines: 1–3 m/s (3–10 ft/s). Pump suction lines run slower, around 0.5–1 m/s.
Output
| Property | Value |
|---|---|
| No data yet | |
| Nominal size | Inside diameter (mm) | Velocity (m/s) | Velocity (ft/s) | Fit |
|---|---|---|---|---|
| No data yet | ||||
Actual velocity at your flow rate in each standard pipe. Sizes at or above the required diameter keep velocity at or below your target.
More ways to use this tool
REST API
curl -X POST https://api.iotools.cloud/v1/tool/pipe-size-from-flow-velocity-calculator \
-H "Authorization: Bearer YOUR_API_KEY" \
-H "Content-Type: application/json" \
-d '{
"flowRate": "100",
"flowUnit": "lpm",
"velocity": "2",
"velocityUnit": "mps"
}'Swap in your own key from your account. The tool's fields are the body — no wrapper.
Ask an AI agent
Use the IOTools `pipe-size-from-flow-velocity-calculator` tool (Pipe Size From Flow Velocity Calculator) on this input:
YOUR_INPUT_HEREPaste this at any agent connected to the IOTools MCP server, then add your input.
Embed widget
<iframe
src="https://iotools.cloud/embed/pipe-size-from-flow-velocity-calculator/"
width="100%" height="520" frameborder="0" scrolling="no" loading="lazy"
title="Pipe Size From Flow Velocity Calculator — iotools.cloud"
sandbox="allow-scripts allow-forms allow-same-origin allow-downloads allow-popups allow-popups-to-escape-sandbox"
allow="clipboard-write"
style="width:100%;border:1px solid #e5e7eb;border-radius:12px;overflow:hidden"></iframe>
<script src="https://iotools.cloud/embed.js" async></script>Drop this into your own page — free, no key required, just a link back.
| Cost per API/MCP call | From 5 credits |
|---|---|
| Need more credits? | View pricing |
Also available with
Guides
The Pipe Size From Flow Velocity Calculator works backwards from the flow you need to move and the velocity you want to keep it at, and tells you how big the pipe has to be. Enter a volumetric flow rate and a target velocity and it returns the required flow area and inside diameter (in mm and inches), then lists every standard Schedule 40 size with the velocity you would actually get.
How to use it
- Enter the flow rate and pick its unit — L/min, L/s, m³/h, m³/s, US GPM or CFM.
- Enter the target velocity in m/s or ft/s.
- Read the required inside diameter, the nearest standard size, and the table of real velocities for each nominal size.
The formula
Continuity gives the flow area directly: A = Q / V. For a round pipe A = π·D² / 4, so the required inside diameter is D = √(4·Q / (π·V)).
What velocity should I design for?
Typical water supply lines run at 1–3 m/s (3–10 ft/s). Pump suction lines are kept slower, around 0.5–1 m/s, to avoid cavitation, while pump discharge lines are often 1.5–3.5 m/s. Higher velocities mean smaller, cheaper pipe but more friction loss, noise and water hammer risk. To check what a given pipe delivers, use the Pipe Flow Velocity Calculator.
Which standard size is picked?
The "nearest size" is the smallest Schedule 40 steel pipe whose actual inside diameter is at least the required diameter, so velocity stays at or below your target. Other materials and schedules (PVC, copper, Schedule 80) have different bores — use the required diameter to match against their catalogue.
Everything runs in your browser; no inputs are sent to a server.