From this site

One project, every trade

Each calculator adds its lines to a single estimate — consolidated BOM, schedule and cash-flow included.

Open My Project →

Roof Drain Sump Pan Sizing Calculator

Calculate the sump pan area needed around a roof drain pipe, based on pipe diameter and required clearance.

Computed in your browser — nothing you enter is uploaded. Figures are presented for United States against IRC 2024, and every formula is cited under regulatory standards below.

Last verified 2026-08-26 · v1.0.0

Market
Imperial · sales tax

Required sump pan area

1.35 ft²

High confidence
Pan diameter
15.75 in

Running these inputs gives 0.13 m² as the required sump pan area. Currently reading for United States under IRC 2024 — pick a different market above and the figures re-cast accordingly.

Estimated cost — your price

This site holds no price list for this material — local prices vary too much to publish honestly. Enter your supplier's price and the result is costed with it.

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 — confirmed fixes become pinned regression tests.

[Schema Verified] Computed in alignment with American Concrete Institute (ACI 318-19) formulas and International Residential Code (IRC 2024) spatial boundaries.

Regulatory standards & verification citations

  • Sump pan diameter = pipe diameter + 2 × clearance; pan area = π × (pan diameter ÷ 2)², standard circular sump pan sizing to provide adequate clearance around the drain pipe for water collection

Your workspace

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 is the sump pan larger than the pipe itself?
The clearance around the pipe gives water room to collect and drain evenly into the pipe opening from all directions, rather than being restricted to a tight gap that could pond or back up.
How is the pan area calculated?
The pan diameter is the pipe diameter plus twice the required clearance (clearance applies on both sides of the pipe), and the pan area is then found using the standard circle area formula on that pan diameter.
Does this account for sump pan depth or drain flow capacity?
No — this calculates only the plan area of the sump pan based on diameter and clearance. Drain flow capacity, pan depth, and overflow provisions should be checked separately against the roof's drainage design requirements.