Water Flow Calculator
Work out how much water flows in a given time — from the flow rate and the time — in litres, US gallons and cubic metres.
Flow rate times time is volume — the maths behind fill times, water bills and tank sizing. This calculator is that multiplication, in whatever flow unit you have.
Enter the rate and the time; the total volume follows.
Your results
Enter your measurements and press Calculate.
Quantities are rounded up to whole tiles, planks, boxes or bags, after the wastage allowance. Cost appears only when you enter a price.
Formula
All lengths are converted to a single unit before the calculation: 1 ft = 0.3048 m, 1 in = 25.4 mm, 1 ft² = 0.09290304 m², 1 yd² = 9 ft². Material quantities are rounded up — you cannot buy part of a tile, plank or bag.
How to use this calculator
- Enter the flow rate and its unit.
- Enter the time in minutes.
- Read the total volume in litres, gallons and cubic metres.
- Use the Copy results button to copy the answer.
Worked example
| Flow rate | 12 L/min |
|---|---|
| Time | 30 minutes |
| Total | 12 × 30 = 360 L |
| US gallons | 360 ÷ 3.785411784 = 95.1 gal |
| Cubic metres | 360 ÷ 1,000 = 0.36 m³ |
Check it by hand: every step above uses the formula in the box. If your numbers match the example inputs but the calculator gives a different answer, please report it via the contact page.
Frequently asked questions
How do I measure my tap's flow rate?
Time how long it takes to fill a known container — a 10-litre bucket in 50 seconds is 12 L/min. Enter that rate here with the time it runs.
What is a normal tap flow rate?
A kitchen tap is typically 6–12 L/min; a shower 6–15 L/min depending on the head. Measure yours rather than assuming — this calculator does the rest.
How long will it take to fill my tank?
Divide the tank volume by the flow rate. A 200-litre tank at 12 L/min takes about 17 minutes. Use the water tank calculator for the volume, then this one for the time.
Is this a substitute for plumbing design?
No. This is a volume calculation for planning. Flow, pressure and code compliance depend on local regulations and real installation conditions — see the safety notice.
Related calculators
Estimates only. Results are for planning. Measure twice, confirm box coverage and tile sizes on the packaging you buy, and follow the manufacturer's instructions. See the disclaimer.