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Pipe velocity and Hazen–Williams friction loss, pipe volume, water-heater energy and recovery time, pressure and head conversion, fall and slope, and a fitting equivalent-length helper. No code values are built in.

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Planning aid; verify against local code and the manufacturer's data; the qualified person on site is responsible. No code values are built in. Nothing leaves this page.

Pipe flow: velocity and friction loss (Hazen–Williams)

Units

Flow, L/s

Inside diameter, mm (not the nominal size)

Pipe length, m

Pipe material (fills C, editable)

Hazen–Williams C factor

Velocity = flow ÷ area. Head loss (SI): h_f = 10.67 · L · Q^1.852 ÷ (C^1.852 · d^4.87), Q in m³/s, d and h_f in metres. The imperial result uses the same equation after unit conversion. C values are commonly quoted figures for clean, new pipe and vary by source and age; they are only starting values. Hazen–Williams is meant for water at ordinary temperatures in turbulent flow. Fittings are not included: add their equivalent length below.

Fitting equivalent length helper

Enter the equivalent length for each fitting type from your fitting maker's data (in the same length unit as the pipe above), or as a number of pipe diameters (L/D). No values are built in.

Straight pipe length

Each fitting's value is a

Fitting (your label)	Quantity	Equivalent length each

Pipe volume

Inside diameter

Diameter unit

Pipe length

Length unit

Water heating: energy and recovery time

Units

Volume, litres

Cold water temperature, °C

Target temperature, °C

Heater input power, kW

Efficiency, % (100 for electric elements)

Energy = volume × ΔT × 4.186 kJ/(kg·K) with 1 litre of water taken as 1 kg (imperial: gallons × 8.34 lb/gal × ΔT °F × 1 BTU/(lb·°F)). Standing losses and draw-off during heating are ignored, so real time is longer.

Pressure converter

Type in any box; the others follow. Head is metres or feet of water at 1000 kg/m³ (1 m = 9.80665 kPa).

psi

bar

kPa

metres of water head

feet of water head

Fall (slope)

Run (horizontal length)

Run unit

Measured drop (fall)

Drop unit

Required slope (from your code or the manufacturer)

Required slope unit

Slope % = drop ÷ run × 100. 1 % = 10 mm/m = 0.12 in/ft. The required slope is whatever you enter; this page does not know any code values.