Grease Trap Sizing Calculator
Calculate the required grease trap capacity for commercial kitchens and restaurants
Installing the wrong size grease trap costs restaurant owners thousands in emergency plumbing repairs, health department fines, and lost revenue during shutdowns. This free calculator determines the exact grease trap capacity your commercial kitchen needs based on fixture flow rates and retention time requirements.
Grease traps (also called grease interceptors) prevent fats, oils, and grease (FOG) from entering municipal sewer systems. When undersized, they overflow during peak kitchen hours, causing backups that flood prep areas and dining rooms. When oversized, you pay for capacity you don't need and face unnecessary installation costs.
Most jurisdictions require grease trap sizing based on flow rate in gallons per minute (GPM) multiplied by a retention factor. The calculation accounts for all fixtures draining into the trap including three-compartment sinks, prep sinks, dishwashers, floor drains, and mop sinks. Our calculator uses industry-standard formulas accepted by health departments and plumbing inspectors across North America.
Restaurant owners who size grease traps incorrectly face consequences beyond plumbing emergencies. Health inspectors can issue violations ranging from $1,000 to $10,000 depending on severity and jurisdiction. Use this calculator to avoid these problems by providing accurate sizing based on your specific kitchen configuration.
Kitchen Configuration
Enter your commercial kitchen fixture details
Standard Trap Sizes
How to Use This Calculator
Start by identifying all fixtures in your commercial kitchen that drain into the grease trap system. Count three-compartment sinks, prep sinks, dishwashers, floor drains near cooking equipment, and mop sinks. Each fixture has a drainage flow rate measured in gallons per minute.
Enter the GPM value for each fixture type. Standard commercial sinks drain at 15-25 GPM, while dishwashers range from 5-15 GPM depending on size. The calculator accepts decimal values for precision and multiplies your total GPM by the appropriate retention factor to determine minimum trap capacity in gallons.
Review the results section showing recommended trap capacity, retention time, and maintenance frequency. These specifications guide equipment selection and help plumbers prepare accurate installation quotes. Save or print the results for permit applications and contractor consultations.
Understanding Grease Trap Sizing
Grease trap sizing relies on calculating peak flow rate, the maximum gallons per minute draining into the trap when multiple fixtures operate simultaneously. This occurs during your busiest service periods when dishwashers run while staff wash pots, drain prep sinks, and clean floor areas.
Most plumbing codes specify retention factors based on establishment type and grease production. Light-grease operations like coffee shops use 1.0 factors. Standard restaurants use 1.5-2.0 factors. High-grease establishments including steakhouses and fried chicken restaurants require 2.0-2.5 factors.
The Uniform Plumbing Code and International Plumbing Code provide sizing tables, but jurisdictions modify requirements based on local sewer infrastructure. Some municipalities require larger capacities than code minimums to reduce FOG discharge into aging sewer systems.
Common Sizing Mistakes
The most frequent error is calculating flow rate based on individual fixture capacity instead of simultaneous use. Restaurant owners add every sink and drain assuming all operate at peak flow simultaneously, when realistic sizing considers how many fixtures actually run at the same time during your busiest 15 minutes.
Many operators underestimate their grease production level, selecting retention factors that don't match cooking methods. A restaurant owner might classify their establishment as "standard" when their menu heavy with fried foods actually requires high-grease specifications, leading to undersized traps that overflow within months.
Forgetting to include floor drains in flow rate calculations causes significant undersizing. When staff mop or hose down floors during closing, these drains contribute substantial GPM that undersized traps can't handle. Always account for all drainage points in your commercial kitchen.