Many people ask us what size grease trap they need to buy for their commercial kitchen.  We tell them the answer is not so simple.  Many townships require a certain size grease trap for their inspection.  Some do not.  If the city you are located in requires a certain size, they will either refer the size as G.P.M. or Gallons Per Minute which is the flow capacity passing through the trap or in Pounds.  Pounds is the capacity the grease trap will actually hold.

However, if they don’t require a certain size grease trap, there is a formula you can use to determine what you need.  We will provide this formula below to help anyone in need of a grease trap:

To Determine the Flow Rate of Each Sink:

  1. Calculate the capacity of the sink in cubic inches:
    ___(length) x ___(width) x ___(depth) = ___cu. in.
  2. Convert the capacity from cubic inches to gallons per minute (GPM):
    ___ cu. in. / 231 = ___ GPM.
  3. Adjust for displacement:
    ___ GPM x 0.75 = ___ GPM.
  4. Result is the flow rate required to drain the sink in one minute.*

Here is an Example:

You have a 3 compartment sink, each compartment is 18″ x 18″ x 14″

  1. 18″ x 18″ x 14″ = 4536 cu. in. x 3 comp. = 13608 cu. in.
  2. 13608 cu. in. / 231 = 58.91 GPM.
  3. 58.91 GPM x .75 = 44.18 GPM.

This would require a 44 G.P.M.  We would go to the next size up which is 50 G.P.M. or 100 lb capacity

If you have a variety of sinks flowing through the grease trap, here is what you would need to do:

  1.  Find out the flow rate for each sink being connected to the grease trap
  2. Take the flow rates for each unit.  Use 100% of the biggest flow rate, 50% of the 2nd biggest and 25% of the 3rd biggest flow rate.
  3. When you add the numbers together, this will give you what size grease trap you  need.

An example is below:

  1.  First sink has a flow rate of 25 G.P.M.
  2.  2nd sink has a low rate of 15 G.P.M.  You would take 50% of this size and it would give you:  7.5 G.P.M.
  3.  3rd sink has a flow rate of 10 G.P.M.  You would take 25% of this size and it would give you:  2.5 G.P.M.
  4. You would then add 25, 7.5 & 2.5= Total Flow Rate of 35 G.P.M.
  5. You will need a 35 G.P.M grease trap or 70 lb trap.

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