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Free Online Grease Trap Sizing Calculator

Size a commercial kitchen grease trap / interceptor from meal count or drainage flow and retention time. IPC basis. Free online tool, no sign-up.

📐 Standard: IPC
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Grease Trap Sizing Calculator
Reference: IPC
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Size a commercial kitchen grease trap / interceptor from meal count or drainage flow and retention time. IPC basis. Free online tool, no sign-up.
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ℹ About This Calculator

A grease trap (interceptor) slows kitchen wastewater so fats, oils and grease can float and be retained instead of blocking the drains. This calculator sizes the trap from the peak drainage flow and the required retention time, or from the meal count, following IPC practice.

Sizing balances flow rate and retention time - the wastewater must stay in the trap long enough (typically a few minutes) for grease to separate and settle. Undersized traps let grease carry through to the sewer; oversized ones can turn septic. Traps also need regular cleaning once the grease and solids layers fill their design capacity.

Grease Trap Sizing Formula

IPC

V = Q × t × f V = grease trap working volume, L
Q = peak drainage flow, L/min
t = retention time, min (typically 2-30)
f = sizing / storage factor for grease + solids
Alternative: V from meals-per-hour × litres-per-meal.

Worked Example

Example: A kitchen with a peak drainage flow of 40 L/min and a required retention of 6 minutes needs a working volume of at least 40 × 6 = 240 L, increased by a storage factor for accumulated grease and solids to around 300-350 L. On a meal basis, a 200-meal service at roughly 8 L/meal drainage gives a comparable interceptor size.

Grease Trap Sizing Reference (IPC)

Grease traps can be sized by drainage flow or by meals served. Indicative interceptor sizes:

Kitchen sizeMeals/dayInterceptor volume
Small caféup to 100100 – 200 L
Restaurant100 – 300250 – 500 L
Large / hotel kitchen300 – 1000500 – 2000 L
Institutional / canteen1000+2000 L+ (multiple units)

Installation & Maintenance

Locate the trap between the kitchen fixtures and the sewer, downstream of a solids strainer, and keep it accessible for cleaning. Only greasy waste (sinks, dishwashers, floor drains) should pass through it - not toilet waste. Clean when the combined grease and solids reach about a quarter of the working depth, typically weekly to monthly depending on load.

Indicative sizes - the local authority and IPC govern the required capacity.

Frequently Asked Questions

How do I size a grease trap for a commercial kitchen? +
Multiply the peak drainage flow by the required retention time (a few minutes) and add a storage factor for accumulated grease and solids. Alternatively size from the meals served - roughly 100-500 L for cafés and restaurants, more for large kitchens.
What retention time does a grease trap need? +
Enough for grease to separate and float - commonly a few minutes at peak flow for compact traps, longer for large gravity interceptors. Too short and grease carries through; too long and the trap can turn septic and smell.
What size grease trap for a restaurant? +
A typical restaurant serving 100-300 meals a day uses a 250-500 L interceptor, though the exact size depends on the peak drainage flow, the appliances connected and local regulations. Use this calculator with your actual flow or meal count.
How often should a grease trap be cleaned? +
Clean it when the combined grease and solids layers reach about a quarter of the working depth - typically weekly to monthly depending on the kitchen load. Neglected traps overflow grease into the sewer and cause blockages and odours.
Where should a grease trap be installed? +
Between the greasy kitchen fixtures and the public sewer, downstream of a solids strainer and accessible for cleaning. Only greasy wastewater (sinks, dishwashers, floor drains) should pass through it; toilet and non-greasy waste bypass the trap.
What is the difference between a grease trap and interceptor? +
They do the same job; the terms differ mainly by size and location. "Grease trap" usually means a smaller unit under or near the sink, while "grease interceptor" refers to a larger in-ground or external tank serving the whole kitchen.
Can I connect a dishwasher to a grease trap? +
Yes, but high-temperature dishwasher discharge can melt grease and let it pass through, so some designs cool or separately handle it. Check that the trap is rated for the discharge temperature and flow of the appliances connected.
What standard covers grease trap sizing? +
IPC covers sanitary pipework and IPC (Plumbing Services) gives grease-interceptor guidance in the US. Local municipal by-laws often set minimum capacities for food premises, which govern the final size.

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