Measure a tap's flow rate using the bucket-fill method — enter a container's volume and how long it takes to fill.
How to Use the Tap Flow Calculator
Time how long it takes to fill a container of known volume at full tap flow.
Enter the "Container Volume (Litres)" and "Time to Fill (seconds)".
Click "Calculate" to see the tap flow rate in L/min and US GPM.
How the Flow Rate Is Calculated
Flow rate (L/min) = Container volume (L) ÷ Fill time (s) × 60. Dividing volume by time gives litres per second, and multiplying by 60 turns that into litres per minute. The US gallons per minute figure is litres per minute × 0.264172, since one US gallon is about 3.785 litres. Use the GPM value only when comparing with American product specifications; Indian fixtures are rated in litres per minute.
Worked Example
A 10-litre bucket takes 45 seconds to fill. Flow = 10 ÷ 45 × 60 = 13.33 L/min, or about 3.52 US GPM. At that rate a 1,000-litre overhead tank would take 1,000 ÷ 13.33 = 75 minutes to fill from this tap, and a 5-minute wash under it would use around 67 litres.
Fill Time for a 10-Litre Bucket and the Flow It Means
Time to fill 10 L
Flow (L/min)
Flow (US GPM)
30 s
20.00
5.28
40 s
15.00
3.96
60 s
10.00
2.64
75 s
8.00
2.11
100 s
6.00
1.59
120 s
5.00
1.32
Getting an Accurate Reading
Check the container's real volume. Bucket markings are often approximate; fill it once with a 1-litre bottle or jug and mark the level you will time to.
Open the tap fully and let it run for a few seconds before you start timing, so trapped air and the initial surge do not distort the result.
Use a phone stopwatch and repeat the test two or three times. Take the average of the readings.
For low-flow fittings such as a basin with an aerator, a 1 or 2-litre jug is easier to time accurately than a large bucket.
Test hot and cold separately on mixers, and test at the time of day you actually use the water, because supply pressure from a municipal line or a pressure pump can change through the day.
What a Low Reading Can Tell You
If every tap in the house is slow, the cause is usually upstream: a low overhead tank (common in top-floor flats, where there is very little height between the tank and the taps), a partly closed main valve, an undersized or scaled supply line, or a weak municipal supply. If only one tap is slow, look at that fitting first: a choked aerator or filter mesh, a worn cartridge, or an angle valve below the basin that is not fully open.
Cleaning the aerator, by unscrewing it and rinsing out sand and scale, is often enough to bring a single tap back to its normal flow. Measure again afterwards to confirm the improvement.
Frequently Asked Questions
Time how long it takes to fill a container of known volume (e.g. a 10-litre bucket) at full flow, then Flow Rate = Volume ÷ Time × 60, converting to litres per minute (LPM).
Most household taps flow at roughly 6-15 LPM, though this varies with your water pressure, tap type, and any flow restrictors/aerators fitted.
It helps diagnose low-pressure complaints, check if a tap meets a fixture's rated flow requirement, or estimate water usage/cost for a task like filling a tank.
Yes. The same method works for any outlet you can direct into a container: hold a bucket under the shower head, or time how long a pump outlet takes to fill a drum of known size. For high flows use a larger container so the fill time is at least 20 to 30 seconds, which keeps timing errors small.
They are related but not the same. Pressure is the force pushing the water; flow is how much comes out. A fitting with a restrictor can give low flow even at good pressure, while a wide open pipe can give decent flow from a low tank. This test measures flow only.