Introduction

A commercial kitchen’s grease trap isn’t only a mandatory plumbing component it’s the frontline defense against:

• Drain clogs

• Sewer backups

• Costly fines

• Kitchen downtime

• Health code violations

• Unpleasant odors

• Hazardous overflow

• Expensive emergency repairs

When the trap is too small, it fills quickly and can no longer separate fats, oils, and grease (FOG). When the trap is too large, you waste money on oversized equipment and frequent unnecessary pumping.

The size has to be just right, based on your real-world kitchen activity and how grease accumulates in your plumbing for restaurants every day.

Understanding the Basics: What Determines Grease Trap Size?

Before you learn how to calculate grease trap size, it’s essential to understand the core factors that influence capacity:

1. Flow Rate (GPM – Gallons Per Minute)

This measures how fast wastewater enters the trap.
Higher flow rate = larger grease trap needed.

2. Total Sink Volume

Calculate the combined volume of all fixtures connected to the trap.

3. Food Type & Oil Output

Some menus release more grease than others.

Examples:

• Fried chicken restaurant: very high FOG

• Vegan café: low to moderate FOG

• Pizza shop: moderate to high FOG

4. Number of Customers Served Daily

More customers = more dishes = more FOG.

5. Kitchen Equipment Connected

• Dishwashers

• 3-compartment sinks

• Floor drains

• Mop sinks

• Wok stations

• Pre-rinse sinks

Each affects the required trap size.

6. Local Building Codes

Cities often set minimum requirements.

7. Frequency of Maintenance

Smaller traps require more frequent cleaning. Larger traps hold more FOG and reduce service intervals.

How to Calculate Grease Trap Size (The Standard Method)

This is the most commonly accepted formula used by plumbers, inspectors, and engineers:

Grease Trap Size Formula

Grease Trap Size (GPM) = Sink Volume × 75% × Drainage Factor

Breakdown:

• Sink Volume: Length × Width × Depth (in inches ÷ 231 = gallons)

• 75%: Accounts for incomplete filling

• Drainage Factor (1 minute): Standard wastewater flow time

Example Calculation

Let’s say you have a 3-compartment sink:

Each compartment:

• 24" × 24" × 14" = 8064 cubic inches

• 8064 ÷ 231 = 35 gallons per compartment

• 3 compartments = 105 gallons total

Apply formula:

Grease Trap Size = 105 gallons × 0.75 = 78.75 GPM

Most inspectors will round up, so you'd need a 80+ GPM grease trap.

Choosing Grease Trap Size by Kitchen Type (Complete Guide)

Different kitchens generate different levels of grease, waste, and water usage. Below is a detailed breakdown.

1. Small Cafés & Coffee Shops

These kitchens typically serve pastries, sandwiches, breakfast plates, and light foods.

Average Needs:

• Light FOG output

• Small dish load

• Minimal frying

Recommended Grease Trap Size:

20–50 GPM (10–30 lbs)

Why This Works:

These facilities don't release heavy oils. A compact under-sink unit usually meets both performance and compliance needs.

2. Fast-Food Restaurants

These kitchens turn over thousands of meals per week, often with deep fryers and high oil usage.

Average Needs:

• Heavy FOG

• Continuous dish cycles

• Multiple sinks

Recommended Grease Trap Size:

100–150 GPM (100–200 lbs)

Why This Works:

Fast-food kitchens are grease-generating powerhouses. Undersizing a trap leads to constant clogs and daily performance problems.

3. Full-Service Restaurants

These kitchens use ovens, fryers, sauté stations, and dish areas.

Average Needs:

• Medium to high FOG

• Multiple plumbing lines

• Steady guest traffic

Recommended Grease Trap Size:

75–120 GPM (70–150 lbs)
Large in-ground units are common.

4. High-Volume Buffets & Hotels

Buffets create extremely high grease output due to constant cooking.

Average Needs:

• Very high FOG

• Multiple sinks & dishwashers

• Large quantities of food waste

Recommended Grease Trap Size:

150–250 GPM (200–300 lbs)

Why This Works:

These kitchens require industrial-grade traps to avoid overwhelming the plumbing.

5. Food Trucks & Mobile Kitchens

Even though they're small, they often produce lots of grease.

Average Needs:

• Medium-high FOG

• Limited plumbing

• Tight space constraints

Recommended Grease Trap Size:

10–20 GPM (5–20 lbs)

Why This Works:

Size must balance mobility and performance.

6. Bakeries

Bakeries produce less grease than restaurants but more than coffee shops.

Average Needs:

• Light to moderate FOG

• Continuous washing cycles

Recommended Grease Trap Size:

20–50 GPM (20–50 lbs)

How Trap Size Affects Commercial Kitchen Setup Cost

Choosing the right trap size can have a big impact on commercial kitchen setup cost. Larger traps cost more, require more labor to install, and may need more extensive plumbing.

Cost Factors:

• Trap size

• Installation complexity

• Local building codes

• Concrete cutting (for in-ground traps)

• Maintenance frequency

An oversized trap means unnecessary expenses; an undersized trap causes constant repairs. Selecting the correct size keeps startup costs low and long-term costs predictable.

Plumbing Requirements for Restaurants Based on Trap Size

Commercial plumbing must handle:

• High temperature water

• Heavy food solids

• Detergents

• Continuous flow

When grease traps are improperly sized, plumbing for restaurants fails due to:

• Slow drains

• Blockages

• Sewer backups

• Pressure buildup

• Water flow imbalance

Correct sizing ensures:

• Smooth wastewater flow

• Optimal FOG separation

• Lower maintenance costs

• Compliance with health inspections

• Reduced wear on pipes

Understanding Local Regulations for Grease Trap Sizing

Most U.S. cities require:

• Minimum size (often 20–30 GPM)

• Maximum grease storage limits

• Regular cleaning (monthly or quarterly)

• Documentation logs

• Approved FOG disposal

Failing inspections often comes down to one issue:
Trap is too small for the kitchen’s real usage.

Many restaurants avoid violations by choosing sustainable, compliant systems. You can explore additional information on eco-friendly kitchens and long-term compliance in this internal guide:
👉 Sustainable Kitchen Practices

Using Menu Type to Choose Grease Trap Size

Your menu directly affects FOG volume.

High Grease Menus:

• Fried foods

• Burgers

• Steaks

• BBQ

• Breakfast meats
  Require larger traps

Medium Grease Menus:

• Pasta

• Grilled items

• Pizza
  Moderate trap size

Low Grease Menus:

• Salad bars

• Smoothies

• Vegan or fresh meals
  Small traps are sufficient

Restaurants that clean regularly and use sustainable waste systems enjoy lower long-term costs. See more benefits of clean kitchen systems here:
👉 Benefits of a Clean Kitchen

Real-World Example: Choosing Trap Size by Scenario

Scenario #1: Small Café

• 1 three-compartment sink

• Low grease menu
  30 GPM trap is sufficient

Scenario #2: Medium Pizza Restaurant

• 1 dishwasher

• 2 sinks

• Moderate oil use
  75 GPM recommended

Scenario #3: Large Fry Kitchen

• Multiple fryers

• Large dishwashing line
  150+ GPM is required

Maintenance Frequency Based on Trap Size

Small Traps (10–50 GPM):

Every 2–4 weeks

Medium Traps (50–100 GPM):

Every 1–2 months

Large In-Ground Traps (100–250+ GPM):

Every 3 months

Bigger traps aren’t “maintenance-free” they simply need service less often.

Tips to Ensure Your Grease Trap Size Performs Efficiently

✔ Train staff on what NOT to put down drains

✔ Pre-scrape dishes

✔ Install proper strainers

✔ Schedule routine pumping

✔ Track FOG levels weekly

✔ Use biodegradable cleaners

✔ Monitor flow rate changes

A trap that’s perfectly sized but poorly maintained still fails.

Why NW Grease Is the Best Partner for Grease Trap Sizing & Maintenance

NW Grease provides:

• Expert sizing assistance

• Professional installation support

• Regular pumping

• Eco-friendly waste management

• FOG reporting for compliance

• Emergency service

• Customized maintenance plans

We help restaurants avoid fines, shutdowns, and plumbing failures by ensuring traps are properly sized, installed, and maintained.

Final Thoughts: The Right Grease Trap Size Protects Your Entire Kitchen

A grease trap isn’t just another piece of equipment it’s a critical safeguard for your kitchen’s plumbing, cleanliness, compliance, and daily operations. When sized properly, it prevents disasters and supports long-term sustainability.

Choosing the right trap size helps restaurants:

• Avoid clogs and backups

• Reduce maintenance costs

• Stay compliant

• Enhance plumbing efficiency

• Support environmental goals

• Improve kitchen workflow.