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Sump Pump Size Chart
Quick answer: A sump pump size chart groups pumps by horsepower and shows typical flow at a realistic head, such as 10 feet. Roughly: 1/4 HP suits light seepage, 1/3 HP most average basements, 1/2 HP wetter lots or higher lifts, and 3/4 HP heavy inflow. Always confirm with the specific pump's published curve.
How to read this chart
The chart below is a planning summary, not a product catalogue. It shows the ranges you will commonly see on residential pump spec sheets when you look up flow at 10 feet of total dynamic head rather than at zero. Ten feet is a useful reference because a typical basement lift of seven to nine feet plus friction lands there. If your head is higher, flow drops; if it is lower, flow rises. Treat each range as "what to expect" and then check the manufacturer's own table.
| Horsepower class | Typical GPH at 10 ft (planning range) | Typical shut-off head | Common situation |
|---|---|---|---|
| 1/4 HP | 800–1,800 | 15–20 ft | Light seepage, low lift, dry lots |
| 1/3 HP | 1,500–2,600 | 18–25 ft | Average basement, 7–10 ft lift |
| 1/2 HP | 2,200–3,600 | 22–30 ft | Wetter lots, higher lift, long runs |
| 3/4 HP | 3,000–4,500 | 25–35 ft | High water table, heavy inflow |
| 1 HP | 3,600–5,500 | 30–40 ft | Very high inflow or tall lift |
The ranges overlap on purpose. A well-designed 1/3 HP pump can outperform a cheap 1/2 HP pump at 10 feet. This is why a chart by horsepower is a starting point only.
Matching pit size to pump size
A pump also has to suit the pit it lives in. Small pits hold less water per inch, so a powerful pump empties them in seconds and restarts often. Short cycles wear out switches and motors and can overheat small units. Use the pit calculator to find your gallons per inch and compare.
| Pit inside diameter | Approx. gallons per inch | Notes |
|---|---|---|
| 14 in | 0.67 | Tight; vertical switch or pedestal often required |
| 18 in | 1.10 | Common older pit; watch cycle length with 1/2 HP |
| 20 in | 1.36 | Reasonable for most 1/3 HP pumps |
| 24 in | 1.96 | Comfortable for 1/2 HP and room for a backup pump |
| 30 in | 3.06 | Large basin; long cycles, good for high inflow |
Gallons per inch is π × (diameter ÷ 2)² ÷ 231. These values ignore the volume taken by the pump itself, which slightly reduces usable capacity.
Discharge size by flow
Most residential sump pumps have a 1½-inch discharge. Higher-capacity pumps may have 2-inch outlets. Reducing the pipe below the pump's outlet size adds friction and noise. The discharge pipe calculator checks velocity for a given flow, and many plumbers aim for roughly 2–8 feet per second in the discharge line to avoid both sediment settling and excessive water hammer.
Worked example
A homeowner has an 18-inch pit holding about 1.1 gallons per inch and a measured storm inflow of 300 GPH. Their discharge head is about 10 feet. The chart suggests a 1/3 HP pump will deliver roughly 1,500–2,600 GPH at that head — far more than needed. The question then is cycle length: with an 8-inch pump-on/pump-off range, the pit holds about 9 gallons between cycles. At 2,000 GPH (about 33 GPM) the pump empties that in around 16 seconds, then waits about 1.8 minutes for 300 GPH of inflow to refill it. That is roughly 30 starts an hour in a storm — acceptable for many pumps, but a reason to prefer a model with a wider switch range or to ask a plumber about a larger basin.
Illustrative note (2026-10-29): Chart ranges and this example were compiled on 2026-10-29 as illustrative planning figures. They are not taken from any single manufacturer and do not represent tested performance of a specific pump.
What the chart does not tell you
- Build quality: cast iron versus thermoplastic housings, and how well they shed heat.
- Switch type: tethered float, vertical float, diaphragm or electronic sensor — each has different pit-size needs.
- Duty rating: some economy pumps are not meant for continuous running.
- Solids handling: sump water carries sand and grit; impeller design matters.
- Warranty and service: a longer warranty often signals a more robust motor.
Choosing between two classes
If your duty point falls between classes, look at the curves for one pump in each class at your head. Prefer the smaller pump if it clears your target with margin and your pit is small. Prefer the larger pump if your measured inflow already came close to the smaller pump's capacity, your head is near its upper range, or the basement is finished and the consequences of falling behind are expensive. In either case a backup system and an alarm add more protection than one extra size step.
Seasonal differences matter
Flow requirements in a cold climate often peak during spring melt rather than summer storms, while coastal and southern homes may see their highest inflow during tropical rain events. Size for the season that fills your pit fastest and recheck after major landscaping changes.
Frequently asked questions
Why do boxes list such high GPH?
The headline figure is usually at 0 feet of head, where no real basement operates. Look for the 10-foot figure.
Is 3/4 HP overkill for a house?
Often, unless inflow is very high or the lift is tall. Oversizing can shorten pump life in a small pit.
Does the chart apply to effluent or sewage pumps?
No. Those are different products with different code rules; consult a licensed plumber.
Related pages
Using the chart when buying a replacement
If you are replacing a pump that worked well for years, the simplest path is to look up its model number, find its flow at 10 feet, and choose a replacement in the same band. If the old pump ran nonstop during storms, move up one row. If it cycled every few seconds, consider staying in the same class but choosing a model with a wider switch range, or ask a plumber whether the basin can be enlarged. Bring the chart, your pit diameter and your head estimate to the store or to your plumber so the conversation starts from measurements rather than from the biggest number on the shelf.