Measured inflow: — GPM | Friction loss: — ft | Basin volume: — gal
Battery Backup Sizing
Select Battery Backup to size a battery.
Result Summary
| Recommended pump | — |
| Capacity needed | — |
| Total dynamic head | — |
| Measured inflow | — |
| Backup battery | — |
Common Pump Size Chart (approx. at 10 ft head)
| Horsepower | Typical capacity | Suited to |
|---|---|---|
| 1/3 HP | ~1,500 GPH | Most homes, moderate lift |
| 1/2 HP | ~2,500 GPH | Higher water table, longer runs |
| 3/4 HP | ~3,500 GPH | Heavy inflow or high lift |
| 1 HP | ~4,500 GPH | Severe inflow, deep basements |
Head Height Performance (typical 1/2 HP)
| Total head | Capacity |
|---|---|
| 0 ft | ~3,600 GPH |
| 5 ft | ~3,000 GPH |
| 10 ft | ~2,500 GPH |
| 15 ft | ~1,800 GPH |
| 20 ft | ~1,000 GPH |
Every pump loses capacity as head rises. Always check the pump curve at your total dynamic head, not the headline GPH.
What Size Sump Pump Do I Need?
Sizing a sump pump means matching two things: how fast water enters the pit, and how hard the pump must work to push it out. The fastest way to measure inflow is a rise-rate test during heavy rain: with the pump off, time how many inches the water rises per minute, then multiply by the gallons your basin holds per inch. The pump must comfortably exceed that peak inflow, with a safety margin, and still deliver that flow at your total dynamic head. The calculator above does this and recommends a horsepower based on typical pump curves.
Sump Pump GPH vs Head Height
A pump rated for 3,000 gallons per hour does not move 3,000 GPH in your basement. That headline number is usually measured at zero lift. As the pump pushes water higher and through pipe and fittings, capacity drops sharply, which is why total dynamic head matters more than the box rating. Total dynamic head is the vertical lift plus friction loss in the discharge pipe and fittings. Read the pump curve at your actual head to find real-world capacity, and size up if you are near the curve limit.
Battery Backup Sump Pump Sizing
Storms that flood basements often knock out power, exactly when the pump is needed most. A battery backup runs a DC pump from a deep-cycle battery. Size the battery in amp-hours for the runtime you want during an outage: estimate how much the backup will cycle to keep up with inflow, multiply by the pump current draw and your target hours. Most homes use a 75 to 100 amp-hour deep-cycle battery for several hours of storm protection; heavy inflow or long outages call for more capacity or a second battery.
Frequently Asked Questions
1/3 or 1/2 HP? 1/3 HP suits most homes with moderate lift. Step up to 1/2 HP or more for high water tables, long discharge runs, or deep basements.
What is total dynamic head? The vertical lift plus friction losses in the pipe and fittings. It is the real load the pump works against.
Do I need a backup pump? If a flooded basement would cause real damage, yes. Power and primary-pump failures are the two most common causes of flooding.
Why does my pump cycle so often? A small basin or oversized pump empties the pit too fast. A larger basin or wider on/off range reduces short cycling and extends pump life.