how to work out cubic feet? To calculate cubic feet, you need to measure the length, width, and height of an object in feet. Then, multiply these three measurements together: Cubic Feet = Length × Width × Height. This formula helps you determine the volume of an object or space, which is essential for shipping, storage, and packaging purposes. For irregularly shaped items, measurements may need to be taken at the widest points, or you can use a more complex formula.