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Pipe calculator: copper or plastic pipe, clips, fittings, solder, lagging and a flow check
Work out the pipe, clips, fittings, solder or inserts, PTFE and lagging for a run of copper or plastic, and check the bore will carry the taps and showers on it at a sensible speed. It uses the same approach as TradeCalc in the Hard Hat Way app, with clip spacing from the copper tube and Speedfit guides, solder counted per joint, and BS 6700 outlet flows for the velocity check.
What you need
Pipe
- Pipe: 15 mm copper
- 22.0 m20 m plus 10% waste
- Lengths to buy (3 m)
- 8 × 3 m lengthscopper is sold in 3 m (and 6 m) straight lengths
- Effective length for pressure drop
- 31.4 mthe fittings add about 11.4 m (guide figures)
Fittings
- Clips (copper, horizontal, every 1.2 m)
- 17 clipstalon clips or Munsen ringsMueller Kuterlon copper tube guide, Table 10
- Fittings (end feed)
- 13 fittings8 elbows, 2 tees, 2 valves, 1 stopcock: 28 joints
- Solder wire (end feed only)
- 0.28 m10 mm of wire per joint × 28 joints, plus a tub of fluxAPMI capillary joint guide
- PTFE tape
- 1 rollthreaded joints only (tap connectors, valves): 3 here, one roll per 10
Lagging
- Lagging: 15 mm bore, 20 mm wall
- 22.0 m11 × 2 m lengths (Climaflex or Armaflex type)Part L: insulate accessible hot pipes; pipelagging.com wall thicknesses
Flow check
- Design flow
- 0.45 l/s1 basin, 1 bath, 1 shower, 1 sink, 1 WC: 0.98 l/s if all ran together, 19.5 loading units with diversityBS 6700 design flows and loading units (CIPHE method)
- Velocity in 15 mm copper
- 3.1 m/stoo fast: keep hot water under 2 m/s to avoid noise and erosion, go to 22 mm (1.4 m/s)Mueller copper guide 0.5–3 m/s; squote 3 m/s cold, 2 m/s hot
- Heating capacity of this bore
- 6 kWat about 1 m/s and 20 K flow-to-return, if this is a heating circuitsquote pipe sizing
Round up to whole packs and bags. Figures include the wastage you chose and match TradeCalc in the app.
For plumbers: turn this into a quote
In the app, TradeCalc hands these quantities straight to ProQuote with your regional material prices, and the customer gets a branded PDF. Free to download.
Or claim your free profile link nowHow the maths works
- Pipe is the straight run plus 10% waste. Copper comes in 3 m (and 6 m) straight lengths, so the calculator rounds up to whole lengths; plastic is shown in 25 m coils.
- Clips on copper follow the copper tube guide (Mueller Kuterlon Table 10): horizontal 1.2 m for 10 and 15 mm, 1.8 m for 22 and 28 mm, 2.4 m for 35 and 42 mm, 2.7 m for 54 mm; vertical 1.8, 2.4, 3.0 and 3.0 m. Plastic sags, so Speedfit clips go every 300 mm (horizontal) or 500 mm (vertical) on 10–15 mm, 500/800 on 22 mm and 800/1,000 on 28 mm, and no closer than 60 mm to a fitting.
- Each fitting has joints: two on an elbow, three on a tee, two on a valve or stopcock. On end-feed fittings the solder is counted per joint, about 10 mm of wire at 15 mm, 15 mm at 22 mm and 22 mm at 28 mm (APMI), so 28 joints in 15 mm use about 0.3 m of wire, not metres of it. Solder ring (Yorkshire) fittings need none.
- PTFE tape is only for threaded joints such as tap connectors and valve bodies, one roll per 10; capillary, compression and push-fit joints do not use it. Plastic pipe needs an insert in every pipe end that goes into a push-fit fitting.
- Equivalent lengths are guide figures for pressure drop, not for buying pipe: at 15 mm about 0.6 m per elbow, 1.0 m per tee, 0.3 m per valve and 4 m per stopcock, scaled by bore ÷ 15.
- Lagging on a hot run or a pipe that could freeze: 20 mm wall on 15 mm, 25 mm on 22 mm, 30 mm on 28 mm and up, in 2 m lengths. Part L asks for accessible hot pipes to be insulated when a boiler or cylinder is replaced.
- The flow check adds up BS 6700 design flows (basin 0.15 l/s, bath 0.30, shower 0.20, sink 0.20, WC 0.13), applies diversity through loading units, and works out the speed in the bore. Keep cold water under 3 m/s and hot under 2 m/s (1–1.5 m/s on heating) or the pipe is noisy and erodes; if it is over, it tells you the next bore that is not.
Worked example
A 20 m horizontal run of 15 mm copper with end-feed fittings, 8 elbows, 2 tees, 2 valves and a stopcock needs 22 m of pipe (8 × 3 m lengths), 17 clips at 1.2 m, 28 joints using about 0.28 m of solder wire, and 1 roll of PTFE for the 3 threaded joints. Lagged at 20 mm wall that is 11 × 2 m lengths. Feeding a basin, bath, shower, sink and WC it needs 0.45 l/s, which runs at 3.1 m/s in 15 mm: too fast, so go to 22 mm.
Questions people ask
How far apart should pipe clips be?
Copper, horizontal: 1.2 m for 15 mm, 1.8 m for 22 and 28 mm, 2.4 m for 35 and 42 mm, 2.7 m for 54 mm; vertical runs can go to 1.8, 2.4 and 3.0 m (copper tube guide, Table 10). Plastic needs far more: Speedfit says every 300 mm horizontal and 500 mm vertical on 10 and 15 mm, 500 and 800 mm on 22 mm, 800 mm and 1 m on 28 mm, and no clip closer than 60 mm to a fitting.
15 mm or 22 mm pipe?
22 mm is the usual size for the cold main, the boiler flow and return and a bath supply, dropping to 15 mm for rads, basins and WCs. On heating, 15 mm carries about 6 kW, 22 mm about 15 kW and 28 mm about 26 kW at 1 m/s. On water, a bath and shower on the end of a long 15 mm run will disappoint: use the flow check above, and keep cold water under 3 m/s and hot under 2 m/s.
How much solder do I need?
Far less than people buy. An end-feed 15 mm joint takes about 8–10 mm of wire, 22 mm 12–15 mm, 28 mm 18–22 mm, so a 250 g reel does a whole bathroom. Count the joints, not the fittings: an elbow has two, a tee three. Solder ring (Yorkshire) fittings have the solder built in and just need flux and heat.
Which pipes need insulating?
Hot water pipes, so the heat gets to the tap and not the floor void, and any pipe in a loft, garage or outside wall where it could freeze. Cold pipes near hot ones are worth lagging too so the cold does not run warm. Use the right bore and a 20 mm wall on 15 mm, 25 mm on 22 mm and 30 mm on 28 mm.
Which plumbing has to be notified to the water company?
Under Regulation 5 of the Water Supply (Water Fittings) Regulations 1999 you must tell the water company before installing a bath over 230 litres, a bidet with an ascending spray or flexible hose, a pump or booster drawing more than 12 litres a minute, a reverse-osmosis unit, a garden watering system (other than a hand-held hose), or the plumbing in a new building or extension. They have 10 working days to consent. An approved contractor (WaterSafe) can self-certify some of it.
Can I do my own plumbing?
Most pipework is not restricted, but anything on the gas side needs a Gas Safe registered engineer, unvented hot water cylinders need a G3 qualified installer and building control notification, and the water-company list above applies. Prices for a plumber vary a lot by area, so get a few quotes.
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