You will need to measure the length and width of your home. You multiply the two numbers together, that will give you the square footage.  Here is a link to a calculator if you need one: https://www.homeadvisor.com/r/calculating-square-footage/

If your home/room has an irregular shape, then you can to take mean of each side e.g
[ w1 + w2 / 2 ] x [ L1 + L2 / 2 ]  ('W' denotes width and 'L' denotes Length) - You can also calculate using this calculator <a rel="nofollow" target="_blank" href="https://www.squarefootagearea.com/calculator/square-footage-calculator/">https://www.squarefootagear...>