Water pipe calculator
Like cable, supply pipe can be estimated from the number of water points and their average distance from the source (boiler, cylinder or meter), plus a reserve.
Your measurements
Result
- Pipe needed (incl. 15% reserve)
- 34.5 m
Includes 15% for bends and connections; fittings are not included.
How the calculation works
- Base length = number of water points × average distance from the source to a point.
- Length to order = base length + 15% for bends, detours and connections.
Worked example
For 6 water points at an average distance of 5 m: 6 × 5 = 30 m, plus 15%, so about 35 m of pipe.
What the calculator assumes
- A water point is a tap or a mixer; the calculation assumes one pipe to each.
When to adjust the result
- Mixers with hot and cold water (basin, shower, sink) have two pipes, so count them twice.
- Pipe is often sold in fixed lengths (for example 4 m bars) — divide and round up.
- Fittings and insulation for hot water pipes are not included.
Planning a water-pipe run
Pipe diameter depends on how many outlets run at once and how long the run is. Long runs to a shower on the top floor need a larger pipe than the short branch to a basin. Keep hot runs short, or the wait for hot water — and the water wasted — grows with every metre.
Insulate hot pipes to save heat and cold pipes where they could freeze or sweat. Fit isolation valves at each appliance and near manifolds so repairs do not mean shutting off the whole house. Pressure-test new work before closing walls or screed, and record the routes with photos.
Frequently asked questions
How much pipe for a bathroom?
Count each hot and cold supply as a point, multiply by the average distance to the source and add 15%.
Should hot water pipes be insulated?
Yes — insulation reduces heat loss and the wait for hot water, and is often required by energy rules.
PEX, multilayer or copper?
PEX and multilayer are quicker to install and resist freezing better; copper is durable and rigid but slower to fit. Use the fittings designed for the chosen system.
Should water pipes go in the floor or the wall?
Both work if pipes are sleeved or insulated and pressure-tested before covering; avoid joints in inaccessible places where possible.