Water flow rate calculator (bucket test)
The calculator needs JavaScript. The worked example, formula and figures below show exactly how it works, so you can do the sum yourself. A guide, not advice. Check your supplier's or maker's figures before ordering.
Short answer
Worked example
| You enter | Value |
|---|---|
| Water collected | 4 L |
| Time to collect it | 15 s |
Flow rate: 16.0 L/min
| Result | Value |
|---|---|
| Flow rate | 16 L/min |
| In litres per second | 0.267 L/s |
| In cubic metres per hour | 0.96 m³/h |
Show the working
- Flow: 4 L ÷ 15 s × 60 = 16 L/min (0.267 L/s)
How it works
- Flow (L/min) = litres collected ÷ seconds × 60
- L/s = L/min ÷ 60; m³/h = L/s × 3.6
- Pressure drop = static pressure − dynamic (running) pressure
Test at the tap nearest the stopcock (usually the kitchen cold tap) with nothing else running, and repeat it two or three times.
Combi boilers, unvented cylinders and power showers each list a minimum flow and pressure: compare with the maker's figure, not a general rule.
Our default (adjustable)
These are typical planning figures and our own allowances, not facts about your product. Change any of them in the calculator to match your bag, pack or tin.
This calculator has no built-in defaults: every figure comes from you or your product's data.
Regulations and standards
- Water Supply (Water Fittings) Regulations 1999 (England and Wales); Scottish Water Byelaws 2014; Water Supply (Water Fittings) Regulations (Northern Ireland) 2009
- Appliance maker's installation instructions (minimum flow and pressure)
Explained: Approved Document G (hot water safety).
The water fittings rules differ: England and Wales (1999 Regulations), Scotland (Byelaws 2014), Northern Ireland (2009 Regulations).