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The peak drainage flow rate from the fixtures connected to the grease interceptor.
Determine total flow rate from the PDI-G101 fixture flow rate tables for each connected fixture (sinks, dishwashers, etc.).
The minimum time wastewater must be retained in the interceptor to allow grease to separate.
PDI-G101 specifies a standard retention time (typically 2 minutes) for hydromechanical grease interceptors.
A multiplier accounting for grease storage capacity needed between service intervals.
Higher-volume or full-service food operations typically use a higher storage factor to extend time between required pump-outs.
Required grease trap capacity
136 gal
Flow rate and storage factor depend on the specific fixtures connected (per PDI-G101 fixture flow rate tables) and food service type — confirm against your local plumbing code's grease interceptor sizing requirements.
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Grease Trap Sizing Calculator (PDI-G101 Method): 136 gal — shown in imperial, US market. The link sets both, so the result they see is the one on your screen.
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How this was calculated
Formula source(s)
- PDI-G101 method: required grease trap capacity = flow rate × retention time × storage factor, the standard plumbing industry method for sizing hydromechanical grease interceptors for commercial kitchen fixtures
Inputs used
- Flow Rate
- 40 gal/min
- Retention Time (minutes, Typically 2 per PDI-G101)
- 2
- Storage Factor (Typically 1.7 for Full-Service Restaurants)
- 1.7
Confidence note: Flow rate and storage factor depend on the specific fixtures connected (per PDI-G101 fixture flow rate tables) and food service type — confirm against your local plumbing code's grease interceptor sizing requirements.
What this calculation does not cover
- A PDI-rated interceptor only performs at its rated flow, and reaching that takes a flow-control fitting this sizing never mentions. The fitting's orifice plus its vent throttles the surge from a pot sink dumping so the water is actually inside the unit for the retention time assumed above; without it the slug blows straight through a correctly sized trap and takes the grease with it. It is the cheapest item in the installation and the one most often omitted.
- What gets connected matters more than the capacity. Dishwasher discharge at 60-80°C re-emulsifies grease so it passes through as a solution and re-solidifies in the sewer downstream, which is why many jurisdictions bar a dishwasher from a small point-of-use interceptor or divert it to a large in-ground one; a food waste disposer fills the same unit with solids that eat the grease storage this factor was meant to buy. Sanitary drainage must never be connected at all.
- The storage factor extends the service interval only until the rule catches up with it. Most authorities require pumping once grease and settled solids reach a quarter of the wetted volume, and many set a maximum interval regardless of size — 90 days is common — so a generously sized unit does not buy an open-ended run between visits, and the manifest for those visits is usually what an inspector asks for first.
- The answer is a liquid volume, which is not how a point-of-use unit is bought. Hydromechanical interceptors are certified as a flow rating with a paired grease capacity in pounds and sold in fixed steps, so this figure has to land on a catalogue model rather than a tank size. A gravity interceptor buried outside is the one specified as a volume, and most codes size that one by a different method again.
Estimated cost — your price
This site holds no price list for this material — local prices vary too much to publish honestly. Enter your supplier's price and the result is costed with it.
Computed in your browser — nothing you enter is uploaded. Presented in US customary units and US trade terminology. Where a formula follows a published standard, that standard and its edition are cited beside it on this page; where none governs, the page says so. Local amendments override model codes — verify against the code in force where you build.
Sources checked 2026-09-06 · in the site-wide review of 2026-09-06 · v1.1.1
Regulatory standards & verification citations1
- PDI-G101 method: required grease trap capacity = flow rate × retention time × storage factor, the standard plumbing industry method for sizing hydromechanical grease interceptors for commercial kitchen fixtures
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