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Sump Pump GPM Calculator

Estimate the minimum pump capacity (gallons per minute) needed for your sump basin's fill rate.

Computed in your browser — nothing you enter is uploaded. Figures are presented in United States units and terminology, and each formula’s basis is cited under regulatory standards below.

Last verified 2026-08-25 · v1.0.0

Market
Imperial · sales tax
1.5 ft
Schematic, drawn to the proportions you entered — not to scale on screen.

Minimum pump capacity

6.47 GPM (minimum)

Check your inputs

This sizes for the basin's fill rate only — also check the pump's rated GPM at your actual vertical lift height (to the discharge point), since GPM drops as lift height increases on every pump's performance curve.

Basin volume at fillable depth
12.94 gal

For the dimensions entered, expect a minimum pump capacity of 6.47 GPM (minimum). Moderate confidence — sound arithmetic, but allow for the variation any real site introduces. Set for United States. The market selector changes the units and the trade terminology; any standard behind the formula is cited under sources.

Add the equipment this sizes

This result is a specification — 6.47 GPM (minimum) — not a quantity. Put the thing it sizes into your project: how many, what you call it, and your supplier’s price.

Preliminary estimate, not certified engineering. This tool produces an indicative quantity calculation for planning purposes only — it is not a certified structural analysis, a guaranteed material takeoff, or a substitute for building department approval. Always verify measurements on-site and have a licensed contractor or structural engineer review any load-bearing, code-sensitive, or safety-critical work before purchasing materials or starting construction. Spotted an arithmetic or standards error? Report it to contact@craftquantities.com with your inputs — a confirmed fix gets a permanent check of its own, so the same mistake cannot come back.

Presented in US customary units and US trade terminology. Where a formula follows a published standard, that standard and its edition are cited beside it on this page; where none governs, the page says so. Local amendments override model codes — verify against the code in force where you build.

Regulatory standards & verification citations

  • Basin volume = pi x radius² x fillable depth, converted to gallons; required pump GPM = basin volume in gallons / target fill time in minutes

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Most jobs need more than one number. Add the calculators you need next and they open right here, underneath this one — your figures stay on screen and nothing is lost to a page change.

Frequently asked questions

Why does GPM matter beyond just 'having a working pump'?
An undersized pump can't keep up with heavy inflow during storms, causing the basin to overflow onto the basement floor — sizing for a fast fill time gives margin for worst-case inflow, not just typical conditions.
Does discharge pipe height affect the pump I should buy?
Yes significantly — every pump's GPM output drops as it has to push water higher (its 'head'). Check the pump's performance curve at your actual vertical lift to the discharge point, not just its GPM rating at zero lift.
Should I get a battery backup pump too?
Worth strongly considering — power outages often coincide with the storms that cause the heaviest sump pump demand, which is exactly when a primary pump without backup power fails you.