All Fusion Subwoofers have an optimum Enclosure Volume which is based on a specific tuning point. To calculate volume you need a calculator and a tape measure and the following formula.
Length (in inches) x Width (in inches) x Depth (in inches) divided by 1728 = volume in Cubic feet.
Length (in Centimeters x Width (in Centimeters) x Depth (in Centimeters) divided by 1000 = volume in cubic litres .
Always allow for the volume of the subwoofer that will be inside the enclosure and the port if applicable. Ensure you measure the inside dimension allowing for the enclosure material thickness.