Pond pump & volume calculator
Enter your pond's size and fish load. We'll estimate the water volume and size the pump, filter, and UV to it, using the one-turnover-per-hour rule the extension services publish.
Your pond
Rough measurements are fine, round to the nearest foot.
Rules of thumb from Penn State & Michigan State Extension pond guidance: turn the pond over once per hour (twice for koi); UV at about 2 watts per 100 gallons for green-water control. Estimates only, your head height and fish load change the real numbers. Always size up, never down.
How we size the pump
The rule the extension services publish is to turn the whole pond over about once an hour, so a 500-gallon pond wants a pump moving roughly 500 gallons per hour. Koi are the exception: they are heavy waste producers, so we double it to a turnover every 30 minutes. The catch is that pump ratings are measured at zero head, with the outlet at water level. Lift that water to the top of a waterfall and run it through a few feet of hose and you can lose a third or more of the number on the box, which is why the calculator gives you a minimum and we tell you to buy above it.
Why the filter and UV scale with the fish
Volume alone does not size a filter, the waste load does. A plants-only pond can run a filter rated to its own volume; goldfish want about 1.5 times; koi want roughly double, because the filter has to process far more ammonia. The UV clarifier is sized to gallons instead of fish, at about 2 watts per 100 gallons for green water, and it only works if the flow through it is slow enough for the light to hit every drop. Oversize the UV and undersize the flow and you still get clear water; do the reverse and you do not.
Round up, never down
Every number here is a floor. Head height, an undersized hose, a long pipe run, and a dirty filter all pull real performance below the sticker, so the safe move is to size up to the next pump and the next filter, never down. A pump that is slightly too strong can be throttled with a valve or a tee; one that is too weak leaves you with murky water and a second purchase.
The gear these numbers size
A calculator only points at three purchases: the pump, the filter, and the UV. These are the ones we reach for at typical backyard volumes.
VIVOSUN
VIVOSUN 5300 GPH Submersible Pond Pump
A high-flow submersible to hit the GPH the calculator gives you. Read the rating as a zero-head number and buy above your target, because a waterfall and hose eat a big share of it.
OASE
OASE BioSmart 5000 Pond Filter
A gravity biofilter is the "filter rated for at least" number in the results. The BioSmart is our default box for a stocked backyard pond, with a cleaning indicator so you know when to rinse it.
Tetra Pond
Tetra Pond GreenFree UV Clarifier
The UV wattage above is for green-water control. Match the bulb wattage to your gallons and match the flow rate the clarifier wants, since water has to pass slowly enough for the UV to work.
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