 Welcome to How to Size an Interior Grease Interceptor. The Wisconsin Administrative Code states that an Interior Grease Interceptor shall be capable of accommodating a flow of at least 15 gallons per minute, but not less than the manufacturer's specifications. For flow rate related to connected capacity, the Code states that three-fourths of the total holding capacity in gallons of all fixtures and devices discharging to an Interior Grease Interceptor shall not exceed the value of the maximum flow rate which the interceptor can accommodate. And for grease holding capacity as related to flow rate, the Code states that the grease holding capacity in pounds shall not be less than double the value of the maximum flow rate which the interceptor can accommodate. To accomplish this Code requirement, the designer must use the following guidelines. First, let's take a look at the Code and then at the sink that the interceptor will be serving. The Code states three-fourths of the total holding capacity in gallons of all fixtures and devices discharging to an Interior Grease Interceptor shall not exceed the value of the maximum flow rate which the interceptor can accommodate. We must determine what three-fourths of the total holding capacity in gallons of the fixture is. To do this, we must determine the volume of the compartments that discharge to the interceptor. To determine the volume of the sink's compartments, we must measure them and multiply the length, width, and depth to find the volume. These sinks are 14 inches by 12 inches by 12 inches which gives us 2,016 cubic inches for each sink. Since there are three compartments, we multiply by three to get 6048 cubic inches. There are 231 cubic inches in one gallon, so we divide 6048 by 231 to give us about 26.18 gallons. Remember that the state Code requires that the flow rate of the grease interceptor be three-fourths of the total holding capacity in gallons of the fixture. The reason we multiply by three-fourths is to allow for the displacement of water from the dishes that will be in the sink. In other words, the sink will only be filled three-fourths full of water, so we only need three-fourths of the sink's volume. Since the sink holds 26.18 gallons, multiply by three-fourths, or 0.75, to get 19.64 gallons. The minimum size grease interceptor would then be equal to, or greater than, 19.64 gallons per minute. The Code also states that the grease holding capacity in pounds must not be less than double the value of the maximum flow rate that the interceptor can accommodate. Since the flow rate we determined was 19.64 gallons per minute, multiply that by two to get 39.28 pounds. The grease interceptor required to serve this fixture must be able to accommodate both 19.64 gallons per minute and 39.28 pounds of grease. Now you try it! Follow along and see if you can figure out the minimum flow rate and capacity needed for an interior grease interceptor connected to the following fixture. Congratulations! You have completed how to size an interior grease interceptor.