Grease Interceptor Sizing Scenario

Use a documented method and see every input. When the required rule or device class is unknown, the responsible answer is not enough information.

Planning tool—not a permit or purchase answer. This page does not select a plumbing code for you. Confirm the adopted rule, device class, manufacturer rating, and approval process with the local authority before buying or installing equipment.

Build a transparent sizing scenario

Method and authority

Device class

Rated peak flowGallons per minute. Use a value supplied by the applicable method or qualified designer.

Retention or drainage timeMinutes. The IPC gravity option supplies 30; user-defined scenarios require your own documented value.

Local authority or project reference

Your source or drawing reference

Measured operational forecast

Scenario result

What this calculation does—and does not do

It shows the arithmetic

The result multiplies the entered peak flow by the applicable time. Inputs, units, method, and assumptions stay visible.

It does not approve equipment

It does not determine local adoption, amendments, fixture routing, product acceptance, installation conditions, or permits.

Sources used on this page

International Code Council

For a gravity grease interceptor, the 2021 International Plumbing Code sizing equation uses the rated peak flow in gallons per minute multiplied by 30 minutes.

Source: 2021 International Plumbing Code, Chapter 10 — 2021 IPC — Section 1003.3.6, Gravity grease interceptors · checked 2026-08-08

Applies to: Gravity grease interceptors only; local adoption, amendments, manufacturer requirements, and approval still control.

Open the official source

Release 2026-08-08.2. Local authorities, equipment instructions, and site safety procedures control where they apply.

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