Grease Trap Calculator
Size a grease trap or grease interceptor based on flow rate, retention time, and fixture count.
Results
Visualization
How It Works
Grease traps (interceptors) separate fats, oils, and grease (FOG) from kitchen wastewater before it enters the sewer. Sizing is based on flow rate, retention time, and hours of operation.
The Formula
Trap Size (gallons) = Flow Rate (GPM) x Retention Time (min) x Storage Factor
Variables
- GPM — Total flow rate from all connected fixtures
- RT — Retention time in minutes (code minimum ~2.5 min)
- SF — Storage factor based on hours of operation
Worked Example
3 fixtures at 20 GPM, 2.5 min retention, 8hr operation: 3 x 20 x 2.5 x 1.0 = 150 gallons = 75 lbs grease trap.
Practical Tips
- Grease traps must be pumped regularly (monthly minimum for restaurants)
- Undersized traps pass grease into the sewer and cause blockages
- Large operations may need in-ground grease interceptors (500-2000 gallons)
- Hot water and detergents reduce grease trap effectiveness