Aquarium filter flow calculator

Catch your filter’s outflow for a timed spell and enter how much water you caught. Add your tank’s water volume to see how many times an hour the filter turns it over. The numbers shown are an example.

For the example: 120.00 GPH coming out of the filter. Turnover for your tank ↓

Worked example: 1 US gal collected in 30 seconds, on a 20-gallon tank. Replace the numbers with yours.

Collected waterCollected volume unitsElapsed time, secondsWater in the tank, US gal (optional)

Only catch the outflow where you can do it safely. Keep plugs dry, never let the pump run dry and don’t change its plumbing to measure it.

Compare a maker’s model ratings (optional)

Add a rating from your own equipment label

Rating typeYour label rating, US GPH

Pump output, circulation or maximum flow?

No model chosen. Your measurement stands on its own.

The flow ratings guide explains why one kind of rating can’t stand in for another. Your measurement shows your filter on the day you measured it, not a maker’s figure.

Measure again after cleaning

Note the amount, the time, the water level and when you last cleaned the filter. New media, a different hose route or another setting changes the reading. A lower reading on its own doesn’t mean the filter is faulty.

Use filter cleaning by the manual for routine service or the troubleshooting guide for an unexpected change. To compare filters before you buy, see the filters.