Plumbing
Water Flow Calculator
Measure real flow rate from a fill test, and see what it means for fixture capacity.
Result
A bucket test measures flow at one fixture with everything else closed. Simultaneous demand elsewhere in the house will reduce it, so test at the worst-case fixture.
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About this calculator
How do I do a bucket test?
Open the fixture fully, time how long a known volume takes to fill, and divide. Use the furthest or highest fixture. That is where problems show first.
What flow rate do fixtures need?
Roughly 2.5 GPM for a shower, 2.2 for a kitchen tap and 1.5 for a bathroom tap under current standards. Older fixtures use considerably more.
The formula
GPM = container volume ÷ fill time in seconds × 60
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