Aquarium Filter Flow Rate Calculator
Find out how many gallons or liters per hour your filter or return pump should move for your tank, and how much rated flow to look for on the box once real-world losses are taken into account.
How to use this calculator
- Enter the tank volume. For a sump system, add the sump volume too; it is counted for the return pump.
- Pick the tank type. This sets the turnover range: how many times per hour the whole volume should pass through the filter or pump.
- Set the expected flow loss. Box ratings are measured with no media and no height to pump against. The calculator divides the real flow you need by what is left after losses, so you know what rating to shop for.
- Optionally estimate head height if your filter or pump has to push water up from under the stand.
Formulas used
The head height rule of thumb comes from Bulk Reef Supply's guide to sizing return pumps. In metric, the lift and horizontal run are in meters and each 90° elbow counts as 0.3 m.
Worked example: 55 gallon community tank with a canister filter
- Real flow target = 55 × 4 to 6 = 220 to 330 GPH
- With 30% loss from media, hoses and lift: 220 ÷ 0.7 to 330 ÷ 0.7 = 314 to 471 GPH rated
- At the middle of that range, the whole tank passes through the filter about every 12 minutes
So a canister rated around 300 to 470 GPH is a good match. A filter rated at 220 GPH would look right on paper but deliver only about 150 GPH in the cabinet.
Metric example: a 200 liter planted tank at 3 to 5 times per hour needs 600 to 1,000 LPH of real flow, or about 860 to 1,430 LPH rated with 30% losses.
Turnover by tank type
There is no official standard, and sources do not agree exactly. These are the defaults used here and where they come from.
| Tank type | Turnover per hour | Notes |
|---|---|---|
| Community freshwater | 4–6× | LiveAquaria and All Pond Solutions both give 4× as the baseline; hobby calculators often use 5–7×. |
| Planted | 3–5× | LiveAquaria recommends slower flow with less surface agitation so plants keep their CO2. Some sources go up to 6×. |
| Betta, fry, shrimp | 3–4× | These animals need very gentle flow. Sponge filters are a common choice. |
| Goldfish, cichlids, messy fish | 8–10× | Heavy waste producers need more mechanical filtration. |
| Reef sump return | 2–5× real flow | Bulk Reef Supply: 5–10× rated, or 2–5× after head loss, counting display plus sump. 10× is about the practical maximum. |
| Reef in-tank circulation | 10–40× | 10× is the classic minimum. Many SPS coral keepers run much more using powerheads. |
Why real flow is lower than the label
Filter ratings assume zero head height, which LiveAquaria calls "optimal conditions". In a real setup, several things eat into that number:
- Lift: a canister under a stand has to push water about 4 feet up. Small filters often lose roughly 4 to 8% of their flow per foot of lift.
- Media: dense or dirty sponges and pads can cut flow by 20 to 40%.
- Plumbing: every elbow, spray bar, long hose and undersized tube adds resistance.
A 30% loss is a sensible default for a canister. Hang-on-back filters lose less because they lift water only a few inches. Powerheads sit in the tank and work close to their rating.
Frequently asked questions
How many GPH filter do I need?
For a typical community tank, aim for the filter to move 4 to 6 times the tank volume per hour in real use. A 55 gallon tank therefore needs about 220 to 330 GPH of actual flow, which usually means buying a filter rated noticeably higher because media, hoses and lift reduce the flow.
Can a filter be too strong?
Yes. Bettas, fry, shrimp and long-finned fish struggle in strong current, and planted tanks lose CO2 when the surface is churned. If a filter is too strong, use a spray bar, a sponge on the intake, or a valve to calm the flow rather than buying a weaker filter with less media.
Why does my filter flow less than the box says?
Ratings are usually measured with no media, no hoses and no height to pump against. Real flow drops with every foot of lift, every bend in the tubing, and as the media clogs. Losses of 30 to 40 percent are common for canister filters.
What is head height?
Head height is the total resistance a pump works against, measured in feet or meters of water. Bulk Reef Supply's rule of thumb is to count each foot of vertical lift as one foot of head, each 90 degree elbow as one foot, each 45 degree elbow as half a foot, and every 10 feet of horizontal pipe as one foot. Look up your pump's flow at that head on its performance chart.
Should I count the sump in the tank volume?
For a sump return pump, yes. Bulk Reef Supply sizes return pumps by the total water volume of the display plus the sump. For filters hanging on or inside the display, use the display volume.
Related calculators
- Aquarium volume calculator: get the real gallons first
- Stocking calculator: how heavy your bioload is
- CO2 calculator: for planted tanks where surface agitation matters
Sources: 4× baseline, slow flow for plants and small fish, and zero-head ratings from LiveAquaria, Choosing the Proper Flow Rate. 4× for tropical tanks from All Pond Solutions. Return pump turnover and head-height rules from Bulk Reef Supply, How to Size a Return Pump. 10× reef rule of thumb from Wikipedia, Reef aquarium. Ranges for betta, goldfish and cichlid tanks and loss percentages from the DIY Smart Home Hub filter turnover calculator.
Last updated: October 2026