Darcy-Weisbach Head Loss Calculator

Head loss equals f times the length over diameter ratio times velocity squared, all divided by two times g, where g is standard gravity 9.80665 m/s2. When you supply a density, the pressure drop is density times g times that head loss, which is the same as f times L over D times density times velocity squared over two.

The calculator is metric. Length and diameter are in metres, velocity is in metres per second and density is in kg/m3. Head loss comes back in metres of the flowing fluid and the pressure drop in pascals. Convert your data to these units first, for example millimetres of pipe bore to metres.

The friction factor f is an input, not something the tool derives. Read it from a Moody chart, or compute it from the Colebrook equation or the explicit Swamee-Jain approximation using the Reynolds number and the relative roughness of the pipe wall.

Head loss is the lost energy expressed as a height of the fluid column in metres, independent of what fluid it is. Multiplying by density and g scales that height into a pressure drop in pascals, so a metre of head is a bigger pressure in water than in air.

No. Untick the density box and the tool returns only the head loss in metres, showing the pressure drop as not available. Head loss alone is enough for a pump head calculation, while the pressure drop is handy when you size against a rated pressure.

The equation carries velocity squared, so friction loss tracks the kinetic energy of the flow. Doubling the velocity multiplies the head loss by four, which is why oversizing a pipe to slow the flow cuts pumping cost sharply.

No. This is straight-pipe friction only. Elbows, tees, valves and entrances add minor losses that you account for separately, either with loss coefficients or by adding an equivalent length to the pipe length you enter here.

Every value must be a positive finite number greater than zero. Zero or negative length, diameter, velocity, friction factor or density is rejected, and the tool asks for numbers if a box is blank or non-numeric.

No. The whole calculation runs in your browser with plain arithmetic, so the pipe figures you type never leave your device and nothing is uploaded to a server.