Result
494 GPH
Look for sump pump capacity around 494 GPH at your required lift.
- Raw water load
- 411 gal/hr
- Lift factor
- 1.2 x
Estimate only. Check sizing, site conditions, product requirements, local rules, and qualified trade guidance before changing equipment or building materials. Read the full disclaimer.
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Optional equipment checkWhat to compare before buying
Compare sump pumps by flow at the calculated lift, horsepower, discharge size, switch type, solids handling, backup power, check valve needs, and basin fit.
Buying checklist
At a glance
- Cost
- Free
- Login
- Not required
- Best use
- Estimate sump pump gallons-per-hour capacity from drainage area, rainfall rate, runoff factor, and vertical lift.
- Output
- Browser result with print and PDF options
- Reviewed
- 2026-08-29
Result summary
Quick answer
With the sample inputs, this calculator returns 494 GPH. Raw water load: 411 gal/hr. Convert the estimated incoming water to gallons per hour, then apply the entered lift and friction factor to set a planning capacity.
Publisher Published by EverydayCalc Editorial Editorial standards and limitations
Each calculator shows its formula and defines the inputs. Worked examples make the math checkable. The page also names the limits that can change the result.
Last calculation review:
Instructions
How to use this calculator
Open the short walkthrough for choosing and checking inputs.
One inch of rain over one square foot is about 0.623 gallons. The calculator applies runoff and lift factors to estimate pump capacity.
Page guide
On this page
Jump directly to the part of the calculator you need.
Calculation details
Formula and methodology
See the exact math used to produce the result.
Target GPH = drainage area multiplied by rainfall inches per hour multiplied by 0.623 gallons per square-foot-inch, runoff factor, and lift factor, rounded up.
Before acting
Assumptions to check
Review the real-world details that can change the estimate.
This is an inflow-screening estimate. Actual pump selection depends on measured inflow, total dynamic head, discharge length and fittings, check valves, pump curves, power, backup capacity, and local drainage conditions.
More guidance Examples, methodology, and planning checks Open the worked example, review notes, reference tables, and practical next checks.
What to verify before acting
Compare the target GPH with the manufacturer's pump curve at the actual vertical lift and discharge configuration, not the zero-head rating.
When to use this calculator
- Screening replacement-pump capacity
- Comparing expected inflow with installed pump performance
- Preparing pump-curve questions before buying
Tips for better estimates
- Measure inflow during a representative wet period when possible.
- Count vertical lift and discharge resistance rather than using pipe length alone.
- Plan backup power and a second-pump strategy separately.
How this calculator is reviewed
This page is checked for inputs, formulas, examples, assumptions, topic fit, and related links. For this calculator, the review also covers measurements, coverage rates, waste allowance, package sizes, prep needs, and rounding rules.
The sample result is covered by automated tests, and the page links to related calculators and, where available, supporting guides so readers can check the assumptions before acting. If a formula, label, or assumption looks off, send the page URL and your inputs through the contact page.
Worked example
Example inputs: Drainage area: 1200 sq ft; Rainfall rate: 1 in/hr; Runoff factor: 0.55; Lift/friction factor: 1.2. With those values, the calculator returns 494 GPH. Look for sump pump capacity around 494 GPH at your required lift.
Project size to estimated materials
| Small room or repair | Measure carefully and buy one practical unit above the estimate |
|---|---|
| Medium project | Check product coverage and round up to full units |
| Large or irregular area | Add a project-specific buffer before buying |
| Patterned or irregular work | Use a larger waste factor before buying |
Example scenarios
- Measure or estimate the drainage area that can actually reach the pit.
- Use a rainfall scenario appropriate to the planning check.
- Compare the result with pump capacity at the real discharge head.
Quick reference chart
| Sample result | 494 GPH |
|---|---|
| Raw water load | 411 gal/hr |
| Lift factor | 1.2 x |
| Best next step | Compare the target GPH with the manufacturer's pump curve at the actual vertical lift and discharge configuration, not the zero-head rating. |
FAQs
Sump Pump Size Calculator questions
Why does vertical lift matter?
Pump flow usually falls as vertical lift and discharge resistance increase, so the advertised maximum flow may not be available in the installed setup.
Should I use the pump's maximum GPH rating?
Use the manufacturer's flow at your estimated head whenever a pump curve is available. The zero-head maximum can overstate installed flow.
Is this a complete drainage design?
No. Confirm pit size, inflow, discharge route, check valve, power, backup plan, code requirements, and site conditions separately.
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Common planning mistakes
Using the zero-head maximum as installed capacity, confusing GPH with horsepower, ignoring lift and pipe resistance, or treating the estimate as a complete drainage-system design.
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