Grease Trap Sizing Calculator

This calculator sizes a grease interceptor for a commercial kitchen by multiplying Flow per Fixture by Number of Fixtures to get a Total Flow Rate, then applying PDI G101's method of flow times retention time times a load-factor multiplier to reach a raw trap volume. That raw volume is rounded up to the nearest of ten standard rated sizes an interceptor manufacturer actually sells (20, 30, 40 gallons and so on up to 500), which is why the Grease Trap Size shown moves in steps rather than smoothly with small input changes. Flow per Fixture and Number of Fixtures affect Total Flow Rate with perfect symmetry: since the formula just multiplies them together, bumping either one by a given percentage raises the flow total by that exact percentage, with neither input outweighing the other.

Retention Time and Load Factor do not touch Total Flow Rate at all -- they only scale the raw trap volume after flow is already fixed, which is also where Cleaning Frequency comes from: the calculator assumes roughly 1% of flow becomes grease and estimates how many weeks pass before that residue fills a quarter of the selected trap. Flow per Fixture is a peak simultaneous-use rate rather than a rate fixtures sustain continuously all day, so Cleaning Frequency assumes that peak rate is only sustained for about 20 cumulative minutes of active use per day -- a rule-of-thumb estimate, not a measured duty cycle -- rather than a full 24-hour day; across the calculator's declared input range this keeps Cleaning Frequency genuinely varying (roughly 1 to 9+ weeks) instead of landing on the same answer regardless of load. This does not replace a local health department's minimum size table, which can set higher requirements than PDI G101 alone.