GPH ratings are measured at zero lift. Real output drops roughly 20–40% once you add hose length and the climb over the pool wall, so the times above are optimistic — size up rather than down. Mesh covers drain on their own and need no pump.
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The formula
gallons = cover area (sq ft) × 0.623 × inches of water weight (lbs) = gallons × 8.34 · snow ÷ its ratio = inches of water
The 0.623 is fixed: an inch of water over a square foot is 0.623 gallons, everywhere, always. Everything else on this page is that number multiplied by your cover and your weather.
A worked example
A 16×32 inground cover is 512 square feet. One inch of rain puts about 319 gallons on it — roughly 2,660 pounds, more than a small car resting on winter fabric. A 350 GPH automatic pump clears that in about an hour of running, which is why the automatic matters more than the capacity: the storm at 2 a.m. is the one that tears covers.
Why covers fail in winter
Almost never the fabric. Water pools at the low point, the weight drags the perimeter inward, water tubes slide off the edge or the safety-cover springs stretch, and the cover dips further — which collects more water. It's a feedback loop with a weekend of inattention as the trigger. A pump that runs on its own breaks the loop.
Standing water is also a genuine drowning hazard on a solid cover, and it's how a cover ends up a mosquito nursery by March. Size the cover itself with the cover size calculator, get the chemicals right with the closing kit calculator, and protect the plumbing with pool antifreeze.
Frequently asked questions
What size cover pump do I need?
Match the pump to how fast water lands, not to your pool's gallons. A typical 16×32 cover takes about 320 gallons per inch of rain — a 350 GPH automatic cover pump clears that in an hour. Small above-ground covers do fine on a 200–350 GPH pump; anything over about 800 square feet of cover in a wet climate wants 1,500 GPH or more.
How much does water on a pool cover weigh?
About 5.2 pounds per square foot per inch of water. One inch across a 16×32 cover is roughly 2,660 pounds. That's why a sagging cover pulls anchors, tears seams, and drags water tubes into the pool — the weight arrives long before the cover looks bad.
Do I need a cover pump with a mesh cover?
No. Mesh drains rain and snowmelt straight through, which is the whole trade (finer debris passes too, so spring water starts a bit greener). Cover pumps are a solid-cover requirement — solid fabric holds every drop that falls on it.
Should I leave the cover pump on all winter?
Yes, if it's an automatic — they idle at a few watts and switch on at about a quarter inch of water. The failure mode that ruins covers is a manual pump nobody remembered during a February thaw. Set it on a flat platform (an upside-down frisbee or pump pad) near the low point so it doesn't sink into the fabric or suck up debris.
Can snow damage a pool cover?
Snow itself is light; the meltwater under it is not. Twelve inches of average snow is about an inch of water — the same 2,660 pounds on a 16×32 cover, arriving all at once during a thaw while the pump may still be frozen in. Clearing heavy wet snow off the middle of a solid cover is worth the twenty minutes.