Every input field, the units it accepts, its validation rule, and the default worked example.
Every input is converted to SI internally before calculation, so you can mix unit systems freely (for example, diameter in inches with length in metres). This page lists each field, its accepted units, and its validation rule.
| Field | Accepted units | Rule |
|---|---|---|
| Flow rate | L/s, L/min, m3/h, m3/s, US gpm | Zero or greater |
| Internal pipe diameter | mm, m, in | Greater than zero — actual bore, not nominal |
| Straight pipe length | m, ft | Zero or greater |
| Absolute roughness (ε) | mm, m, in | Zero or greater; blank = smooth pipe (ε = 0) |
| Fitting K (each row) | dimensionless | Zero or greater |
| Static / elevation head | m, ft | Must be a number when entered — blank is fine (positive = lift, negative = gravity assists) |
| Required residual pressure | kPa, bar, mH2O, psi, Pa | Zero or greater |
| Density | kg/m³ | Greater than zero |
| Dynamic viscosity | Pa·s | Greater than zero |
| Pump efficiency | % | Greater than 0 and at most 100; blank = hydraulic power only |
If any rule is broken, pressing Calculate shows the validation message(s) next to the offending field instead of producing a result. See Warnings & limits for the exact message text.
US gpm uses the US gallon, 0.003785411784 m³).mH2O unit is defined against a
reference water density of 999.972 kg/m³, so 1 mH₂O ≈ 9.806 kPa regardless of the fluid density
you enter for the calculation.mm, m, in); enter the pipe's
real internal diameter, since the tool holds no pipe-size or schedule tables.A fresh session (and New) opens with every field blank. The start panel's Load a worked example button fills these values instead and runs them immediately — see Getting started:
| Input | Value |
|---|---|
| Flow rate | 1 L/s |
| Internal diameter | 25 mm |
| Straight pipe length | 30 m |
| Absolute roughness | 0.0015 mm |
| Fittings (ΣK) | 2× gate valve K 2.0, 3× 90° elbow K 2.7, strainer K 0.3 |
| Static / elevation head | 10 m |
| Required residual pressure | 200 kPa |
| Density | 998.2 kg/m³ (water ≈ 20 °C) |
| Dynamic viscosity | 0.001002 Pa·s |
| Pump efficiency | 60 % |
Roughness and fitting K are user-entered assumptions. The tool intentionally ships no pipe-material or roughness tables, no fitting-K library, no pipe-size/schedule lookup, and no fixture-unit loading. Source your values from project data or a recognised reference and record them in the fitting source note field. See Warnings & limits for the full scope boundary.