# Inputs & units

Source: https://meptools.com/tools/water-pipe-pressure-drop-pump-head/docs/inputs-and-units/

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.

## Fields and accepted units

| 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](/tools/water-pipe-pressure-drop-pump-head/docs/warnings-and-limits) for the
exact message text.

## Unit conversion notes

- **Flow** converts to m³/s (e.g. `US gpm` uses the US gallon, 0.003785411784 m³).
- **Pressure** uses standard gravity **g = 9.80665 m/s²**. The `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.
- **Diameter and roughness** share the same length conversions (`mm`, `m`, `in`); enter the pipe's
  real internal diameter, since the tool holds no pipe-size or schedule tables.

## Default worked example

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](/tools/water-pipe-pressure-drop-pump-head/docs/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 %                                                    |

## What the tool does not contain

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](/tools/water-pipe-pressure-drop-pump-head/docs/warnings-and-limits) for the full
scope boundary.