Measuring square feet seems like it should be an exact science, but---like so many other things in life---there are variables. How you measure square feet depends on why you are measuring them. Many real estate agents base the asking price of a home on square feet, but they may double the square footage of a two-story home that has a loft instead of a full second story, which will complicate things if you are calculating square feet to buy new carpet. Once you figure out why you need that measurement, the rest is easy.
Measure the outside walls of the house. Start at the front and measure across and then measure front to back. Multiply the width by the depth. This will give you a basic idea of the overall size if you are measuring for siding or exterior paint.
Measure the width and length of each room in the house. Multiply each width by each length and then add the totals. This gives you a more accurate measurement of the actual living space.
Draw a basic floor plan if your house is oddly shaped. Break smaller rooms into squares, rectangles or triangles. Multiply the width and length of squares and rectangles. Multiply the base by the height of triangles and then divide by two. Add up all of the totals.
Contact your local association of real estate agents to see if it has measuring guidelines before stating square footage when you list your home for sale.
Do not forget to include the height of each step with the width and depth if you are measuring stairs for carpet.