Grease Trap Sizing Guide
Choosing the right size grease trap is critical for compliance and performance. Too small and it won't work; too large and you're wasting money.
Why Correct Sizing Matters
A grease trap that's too small will fill up too quickly, allowing FOG to pass through into the drains. This causes blockages and puts you in breach of regulations.
An oversized trap costs more to buy and install, takes up more space, and may not work efficiently if the flow rate is too low to create proper separation.
Too Small
- • FOG passes through
- • Frequent cleaning needed
- • Compliance failures
- • Blockages occur
Too Large
- • Higher cost
- • Wasted space
- • May not flow properly
- • Longer retention time
The 25% Rule
A grease trap should be emptied when it reaches 25% full of FOG. Beyond this, separation efficiency drops significantly.
Example: A 100L trap should be emptied when it contains 25L of grease. If your kitchen produces 25L per week, you need weekly servicing.
Factors That Affect Sizing
Several factors determine the right size grease trap for your kitchen.
Number of Meals
The more meals you serve, the more FOG you produce. A busy restaurant needs a larger trap than a small cafe.
Type of Food
Different cuisines produce different FOG levels. Fried food creates more grease than grilled or baked dishes.
Dishwashing Equipment
Dishwashers and pot wash sinks create high flow rates that need larger traps to allow proper separation time.
Operating Hours
Kitchens open longer accumulate more grease. A 24-hour operation needs different sizing than lunch-only service.
Sink Size and Number
More and larger sinks mean higher flow rates. The trap must handle peak flow without allowing FOG through.
Pipework Layout
The physical space available and pipe run length affect what size and type of trap can be installed.
Quick Reference Guide
These are rough guidelines. Always get a professional survey for accurate sizing.
| Meals Per Day | Trap Size | Typical Venues |
|---|---|---|
| 20-50/day | 40-60 litres | Small cafe, coffee shop, kiosk |
| 50-100/day | 60-100 litres | Cafe, small restaurant, pub |
| 100-200/day | 100-200 litres | Restaurant, hotel kitchen |
| 200-400/day | 200-400 litres | Busy restaurant, large pub |
| 400-800/day | 400-800 litres | Large restaurant, hotel, canteen |
| 800+/day | 1000+ litres | Large hotel, hospital, college |
Note: These are minimum sizes. Heavy frying, dishwashers, or long operating hours may require larger traps.
The BS EN 1825 Sizing Method
The British and European standard for grease trap sizing. This is the method professionals use.
The Formula
V = n × Q × t × fNote: This is a simplified explanation. The full standard includes additional factors for different kitchen types, wastewater temperatures, and specific equipment. Always consult a professional for accurate sizing.
Get a Professional Sizing Survey
While guidelines are helpful, nothing beats a professional survey. We visit your site, assess your kitchen, measure flow rates, and recommend the perfect grease trap size for your needs.
- Free, no-obligation site survey
- Accurate sizing calculation
- Consideration of your specific equipment
- Written recommendation with compliance proof
Usually completed within 48 hours
Ready to Get Started?
Get in touch for a free site survey and quote. No obligation, no pressure.