To calculate square footage of rectangular floor space, determine the length and width of the rectangular space in feet, then multiply them together. If floor space is not a perfect rectangle, break the space up into rectangles, calculate the area of each rectangle, and find the sum of the combined areas.

**Break floor space into rectangles if required**If the floor space you are trying to measure is not a rectangle, break the space into several individual rectangles. Ensure that every part of the floor space is contained within only one of the rectangles.

**Determine the length and width of each rectangle's floor space**For floor space that is a single rectangle, find the length and width of the floor in feet. You can measure the length and width with a tape measure, ruler, yardstick or other measuring device. For floor space that is broken into individual rectangles, find the length and width of each rectangle individually. Ensure that each measurement is in feet; for example, express a dimension of 20 feet 3 inches as 20.25 feet. Note that if it is necessary to convert inches into feet, divide the number of inches by 12 to determine the number of feet.

**Multiply the length and width of the rectangle(s) together**Take the length and width in feet of one of your rectangles and multiply the dimensions together. This gives the square footage of that rectangle. If you have multiple rectangles, repeat this process for each rectangle.

**Add the square footages of the rectangles together, if applicable**If you calculated the square footages of multiple rectangles, add all of the square products together. The sum of the square footages is the total square footage of the floor space.