Sump pump sizing
Sump Pump Sizing Calculator: Find Your Horsepower
Instant result calculator Based on Zoeller & Wayne manufacturer performance curves
Based on Wayne Pumps, Zoeller, ASPE Standards
Your sump pit
Adjust any input —the HP recommendation updates instantly.
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Recommended Sump Pump
Est. 2,400 GPH at 10 ft TDH
Default for 24″pit, moderate moisture. Adjust your inputs on the left.
Calculation breakdown
| Pit depth | 24 inches |
| Est. Total Dynamic Head | ~10 ft |
| Moisture level | Moderate |
| Recommended HP | 1/3 HP |
Based on Zoeller & Wayne manufacturer pump curves. TDH increases with pit depth — every extra foot of lift reduces GPH by ~3–5%. Always check the manufacturer's GPH vs TDH chart.
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How This Calculator Works: Sump Pump Sizing Methodology
Our sump pump sizing calculator applies manufacturer performance curves from Zoeller and Wayne Pumps, the two primary residential sump pump manufacturers in the US, combined with industry-standard pump selection methodology.
Horsepower and GPH: the Core Tradeoff
Sump pump capacity is defined by two interacting metrics:
Horsepower (HP): The motor's power rating. Higher HP pumps move more water per minute and can push water higher. Standard residential sizes: 1/4 HP, 1/3 HP, 1/2 HP, 3/4 HP, 1 HP.
GPH (Gallons Per Hour): Actual water movement capacity at a given Total Dynamic Head (TDH). GPH decreases as the vertical lift height increases. A 1/3 HP pump delivering 2,400 GPH at 5 ft of head may only deliver 1,800 GPH at 15 ft of head. The pump performance curve (GPH vs TDH graph) from the manufacturer is the definitive sizing reference.
Pit Depth as a Proxy for Total Dynamic Head
Total Dynamic Head (TDH) is the total height the pump must lift water, including both the vertical lift (static head) and pipe friction losses. Our calculator uses pit depth as the primary TDH proxy, since in most residential installations, the discharge pipe runs from the bottom of the pit to just above ground level:
—12-24″pit depth —~5-10 ft TDH (low head, high GPH)
—24-36″pit depth —~10-15 ft TDH (moderate head)
—36-48″ pit depth —~15-20 ft TDH (high head, lower GPH)
Basements with long horizontal discharge runs or uphill grading have higher effective TDH and may need a larger pump.
Moisture Level —Required GPH
The moisture level determines the minimum GPH needed:
Light seepage: 1,800-2,400 GPH —occasional rain infiltration, pump runs a few times per storm
Moderate: 2,400-3,000 GPH —pump runs several times daily in wet season, typical for most basements
Heavy: 3,000-3,600 GPH —high water table, pump runs frequently, sustained inflow
Severe / flooding: 3,600-5,000+ GPH —standing water risk, requires a primary + battery backup or dual-pump system
These thresholds are derived from Zoeller and Wayne pump curve data with a 20% safety margin.
Submersible vs Pedestal
Submersible: Motor sealed inside the pit, underwater. Quieter operation (sound dampened by water), longer lifespan (5-15 years), more efficient. Best for finished basements where noise matters. Higher cost ($150-400).
Pedestal: Motor mounted above the pit on a column. Easier to inspect and service without entering the pit, longer lifespan (10-25 years), louder. Best for utility spaces. Lower cost ($100-250). Both types are capable of identical GPH at the same HP rating.
Battery Backup: When You Need One
A primary sump pump runs on 120V AC power. When the power goes out during a storm —exactly when the pump is needed most —a battery backup system takes over. Battery backups run on a deep-cycle marine battery (Group 27 or 31) and provide 6-12 hours of intermittent pumping at 1,000-2,500 GPH. They operate at 12V DC and are less powerful than the primary pump. Water-powered backups use municipal water pressure and offer unlimited runtime but require city water and cost $200-350. For homes in flood-prone areas with frequent storms, a dual primary + backup system is the standard recommendation.
Why Sump Pump Sizing Matters
Undersized
- Can't keep up with inflow during heavy storms —water rises while the pump runs continuously
- Basement floods because the pump simply cannot move water out fast enough
- Pump burns out from continuous running —a 1/3 HP pump meant for intermittent use may fail within hours during a sustained storm
- Float switch fails from excessive cycling —the switch mechanism wears out faster than the motor
Oversized
- Short cycles —the pump empties the pit in 5″0 seconds and shuts off. This rapid on/off pattern destroys motors
- Motor burns out prematurely —the #1 cause of sump pump failure is short cycling, not age
- Higher upfront cost —a 3/4 HP pump costs $200″50 vs $100″80 for 1/3 HP, with no benefit for a low-inflow basement
- Uses more electricity per gallon pumped —a larger motor running in short bursts is less efficient than a correctly sized pump cycling normally
5 Common Sump Pump Sizing Mistakes
- Confusing HP with actual GPH. Horsepower is a motor rating, not a water-moving rating. A 1/2 HP pump from Zoeller may deliver 3,600 GPH at 10 ft TDH, while a 3/4 HP budget brand may only deliver 3,200 GPH under the same conditions. Shop by the pump curve, not the HP number on the box.
- Ignoring total dynamic head (TDH). A pump rated "3,000 GPH" on the retail listing typically achieves that only at 5 ft or 10 ft of lift. At 15 ft TDH —common in deep pits —the same pump may deliver only 1,800 GPH. Always read the manufacturer's performance table for your actual lift height.
- Using an undersized discharge pipe. A 1/2 HP pump connected to 1-1/4″pipe creates excessive friction loss that silently chokes flow by 15″5%. The standard discharge size is 1-1/2″ID PVC. For runs over 50 ft, use 2″pipe.
- No battery backup in flood-prone areas. If your flooding risk is tied to storms —and storms correlate with power outages —a single AC-powered pump is a single point of failure. A battery backup ($250″00) is a fraction of the cost of a flooded finished basement ($15,000″0,000).
- Buying the wrong pump type for your space. Pedestal pumps won't fit in crawl spaces with limited vertical clearance. Submersible pumps are the correct choice for finished basements where noise matters. Check fitment before buying.
Common scenarios for sump pump sizing
If your situation matches one of these, jump straight to a detailed guide:
Frequently asked questions
What HP sump pump do I need?
1/3 HP handles most residential basements with normal water tables and under 10 ft of total dynamic head (TDH). 1/2 HP suits deeper pits (10-15 ft TDH) or high water tables. 3/4 HP handles very deep pits (15-20 ft TDH) or heavy inflow. 1 HP is for severe flooding or very deep installations. Always check the manufacturer's GPH vs TDH curve.
How many gallons per hour (GPH) do I need?
Match GPH to your estimated inflow rate. Light seepage: 1,800-2,400 GPH. Moderate: 2,400-3,000 GPH. Heavy: 3,000-3,600 GPH. Severe/flooding: 3,600-5,000+ GPH. GPH ratings are at a specific TDH —a pump rated 3,000 GPH at 5 ft may only deliver 1,800 GPH at 15 ft. Our calculator accounts for this.
Pedestal or submersible sump pump?
Submersible: quieter, sealed motor, $150-400, 5-15 year lifespan. Best for finished basements where noise matters. Pedestal: motor above water, easier to service without entering pit, $100-250, 10-25 year lifespan. Best for utility spaces. Both deliver equivalent GPH at the same HP rating —the difference is installation and maintenance, not performance.
Do I need a battery backup sump pump?
Yes if your area has frequent power outages or your basement floods without power. A battery backup provides 6-12 hours of intermittent pumping at 1,000-2,500 GPH and costs $150-300 plus a deep-cycle marine battery. Water-powered backups use municipal water pressure for unlimited runtime but require city water supply. For flood-prone areas, install both a primary and backup pump.
How deep should my sump pit be?
Standard residential sump pits are 18-24 inches deep and 18 inches in diameter. Deeper pits (30-36 inches) provide more water storage capacity before the pump activates, reducing cycling frequency. Shallow pits under 18 inches require a pump with a lower activation point. The pit should be set below the basement floor slab elevation.
What is Total Dynamic Head (TDH)?
TDH is the total vertical lift the pump must overcome: static head (vertical height from pump to discharge point) + friction head (pipe resistance from length, bends, and check valves). A 10 ft vertical lift with a long horizontal run might be 12-13 ft effective TDH. Every foot of TDH reduces pump GPH by approximately 3-5%.
How long does a sump pump last?
Submersible pumps: 5-15 years depending on cycling frequency, water quality, and debris. Pedestal pumps: 10-25 years since the motor is not submerged. Pumps that cycle on/off every few minutes (short cycling) wear out faster. A properly sized pump that runs for 30-60 seconds per cycle lasts significantly longer than an oversized pump that short cycles.
Why does my sump pump run constantly?
Three common causes: (1) the check valve has failed, allowing water to flow back into the pit, (2) the float switch is stuck in the 'on' position, or (3) your water table is genuinely high and the pump is correctly handling sustained inflow. If the pump has been running nonstop for over 24 hours, check the check valve first —it is a $15 part that fails every 3-5 years.
What size sump pump for a crawl space?
Crawl spaces typically need a smaller pump (1/4 or 1/3 HP) with a low-profile basin since vertical clearance is limited. Pedestal pumps generally do not fit in crawl spaces. Choose a submersible with a low-profile float switch and a sealed basin to prevent radon and moisture entry. GPH requirements are the same as a basement of equivalent water inflow.
Can I install a sump pump myself?
Installing a sump pump involves: breaking the concrete floor to dig the pit, running a dedicated GFCI electrical circuit, installing the discharge pipe through the foundation wall, and ensuring proper drainage slope away from the house. DIY is feasible for experienced homeowners but requires a building permit in most jurisdictions. Hire a licensed plumber for the installation and an electrician for the dedicated circuit.
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