Pipe Pressure Drop Calculator
Calculate the friction-loss pressure drop and head loss along a pipe run from its flow rate (or velocity), diameter, length, material roughness and fluid, using the Darcy–Weisbach equation with a Colebrook-equivalent (Swamee–Jain) friction factor. Works in metric or imperial units and shows the Reynolds number, flow regime and friction factor behind the result.
Input
Flow
Pipe
Internal bore, not the nominal or outside diameter.
Straight-run length. Add equivalent lengths for fittings/valves separately if needed.
Sets the absolute roughness (ε) used in the friction factor. New/clean pipe figures.
Fluid
Presets are at 1 atm. Viscosity is strongly temperature-dependent — pick the closest.
Output
| Property | Value |
|---|---|
| No data yet | |
| Material | Roughness (mm) | Roughness (in) | This Pipe |
|---|---|---|---|
| No data yet | |||
Typical absolute roughness for new/clean pipe, for reference.
More ways to use this tool
REST API
curl -X POST https://api.iotools.cloud/v1/tool/pipe-pressure-drop-calculator \
-H "Authorization: Bearer YOUR_API_KEY" \
-H "Content-Type: application/json" \
-d '{
"inputMode": "flow",
"flowRate": "100",
"flowUnit": "lpm",
"pipeDiameter": "50",
"diameterUnit": "mm",
"pipeLength": "100",
"lengthUnit": "m",
"material": "steel",
"fluid": "water20"
}'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-pressure-drop-calculator` tool (Pipe Pressure Drop 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-pressure-drop-calculator/"
width="100%" height="520" frameborder="0" scrolling="no" loading="lazy"
title="Pipe Pressure Drop 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
Every metre of pipe a fluid moves through costs some pressure to friction against the wall. This calculator works out that loss — in pascals, kPa, bar and psi, plus the equivalent head loss in metres and feet — from the flow (or velocity), the pipe's geometry and material, and the fluid, using the Darcy–Weisbach equation.
How to use it
- Enter what you know: a volumetric flow rate (L/min, L/s, m³/h, m³/s, GPM or CFM) or a mean velocity directly.
- Enter the pipe's inside diameter (the internal bore, not the nominal size) and its run length.
- Pick a pipe material — PVC, copper, commercial steel, galvanized steel, cast iron, concrete or riveted steel — to set the absolute roughness used in the friction factor, or choose Custom roughness and type your own.
- Pick a fluid preset (water, seawater, air, ethanol, oil, glycerin) or enter a custom density and viscosity.
The result gives the pressure drop and head loss, plus the Reynolds number, flow regime and friction factor that produced them, and a reference table of typical roughness values for common pipe materials.
The formula
ΔP = f · (L/D) · (ρV²/2), the Darcy–Weisbach equation, where f is the dimensionless friction factor, L the pipe length, D the inside diameter, ρ the fluid density and V the mean velocity. Head loss is h_f = ΔP / (ρg).
The friction factor depends on the flow regime:
Laminar (Re < 2300): f = 64/Re — exact, no dependence on roughness.
Turbulent (Re > 4000): f from the Swamee–Jain equation, an explicit approximation to Colebrook–White accurate to within about 1%, avoiding an iterative solve:
1/√f = -2 log₁₀( ε/(3.7D) + 5.74/Re^0.9 )
Transitional (2300 ≤ Re ≤ 4000): genuinely unstable in practice — the calculator applies Swamee–Jain here too, as the conventional estimate, but treat results in this band as approximate.
What this doesn't include
This is the major (friction) loss along a straight run only. It does not add minor losses from fittings, valves, elbows or entrance/exit effects — for those, either convert each fitting to an equivalent pipe length and add it to the run length, or apply a separate loss-coefficient (K) calculation and add the result.
Privacy
Everything runs in your browser. No flow rates, dimensions or fluid properties are sent anywhere.
Related tools
Need the Reynolds number and flow regime on their own, with more fluid presets and duct/rectangular cross-sections? See the Reynolds Number Calculator. To go the other way — from a known velocity or flow rate to the pipe size — see the Pipe Flow Velocity Calculator. For unit changes outside what's built in here, the Pressure Converter and general Unit Converter cover the rest.