How to Choose the Right Grease Trap Size for Your Restaurant: A Step‑by‑Step Guide

A grease trap that’s too small clogs faster than a busy lunch line, while an oversized unit eats up money and space for no good reason. Getting the size right is one of those “small” decisions that can save you headaches, fines, and a lot of extra grease.

Why Size Matters Right Now

The health department is tightening inspections, and waste‑disposal fees are climbing. If your trap is the wrong size, you’ll see more frequent pump‑outs, higher service bills, and a higher chance of a violation notice. In short, the right size keeps the kitchen running smooth and the regulator happy.

Step 1 – Know Your Kitchen’s Flow Rate

What is Flow Rate?

Flow rate is the amount of water that runs through your sink, dishwasher, and fryers each minute. It’s measured in gallons per minute (GPM). Think of it as the speed at which water carries grease away from the pots.

How to Measure It

Turn on the faucet you use most for cooking water.
Place a bucket under the flow and time how long it takes to fill a known volume (say 1 gallon).
Calculate: GPM = volume (gallons) ÷ time (minutes).

If you have multiple sinks, add their GPM together. For a typical 50‑seat diner, you’ll see 8‑12 GPM. A high‑volume fast‑food kitchen can push 20‑30 GPM.

Step 2 – Estimate Grease Production

The Grease Factor

Not all water carries the same amount of grease. Fryers, grills, and sauté stations dump more oil than a salad prep station. A rule of thumb from the EPA is that about 0.5% of the total water flow will be grease.

Quick Calc

Grease (gallons per hour) = Total GPM × 0.005 × 60

Example: 15 GPM kitchen
Grease = 15 × 0.005 × 60 = 4.5 gallons per hour

If you run a lot of deep‑fryers, bump that number up by 25% to be safe.

Step 3 – Pick the Right Capacity

Capacity Basics

Grease traps are rated by the amount of grease they can hold before they need cleaning, usually expressed in pounds or gallons. Most manufacturers list a “capacity” that matches a specific flow rate.

The 10‑to‑15 Rule

A well‑designed trap should hold at least 10‑15% of the daily grease load. This gives a buffer for peak hours and prevents early overflows.

Formula:
Required Capacity (gallons) = Daily Grease Load × 0.12 (average of 10‑15%)

Example

Daily grease load = 4.5 gal/hr × 12 hrs = 54 gallons
Required capacity = 54 × 0.12 ≈ 6.5 gallons

In practice, you’d round up to the next standard size – often a 7‑gallon unit.

Step 4 – Check Local Regulations

Every city has its own code. Some require a minimum capacity based on the number of seats, while others tie it to the square footage of the cooking area. Grab your local health department’s guide (often a one‑page PDF) and verify that the size you’re eyeing meets or exceeds the mandated minimum.

Step 5 – Factor in Space and Maintenance

Physical Footprint

A 7‑gallon trap might be a compact, rectangular unit that fits under a prep sink. A 30‑gallon model could need a dedicated closet. Measure the space you have before you order.

Pump‑Out Frequency

Even the right size will need cleaning. The EPA suggests a pump‑out when the trap is 25% full. With our 7‑gallon example, that’s about 1.75 gallons of grease. Knowing this helps you schedule service and budget for it.

Step 6 – Choose the Right Type

There are two main families:

Passive (gravity) traps – simple, no power needed, good for most restaurants.
Automatic (mechanical) traps – use a pump or motor to move grease, useful when space is tight or flow is irregular.

If you have a small kitchen with limited headroom, an automatic unit might be the only way to fit the required capacity.

Step 7 – Get a Professional Opinion

Even with the math, a seasoned installer can spot quirks you might miss: a hidden line that adds extra flow, or a venting issue that reduces efficiency. I always recommend a short site visit before you sign off on a purchase. It’s a cheap insurance policy.

Quick Checklist

Measure total GPM of all cooking water sources.
Estimate daily grease load using the 0.5% rule.
Apply the 10‑to‑15% capacity buffer.
Verify local code minimums.
Confirm you have room for the unit.
Decide between passive or automatic.
Schedule a professional review.

Getting the size right the first time pays off in fewer service calls, lower fees, and a cleaner kitchen. It’s a small math problem that protects a big operation.