Square Foot
If your home has different shapes, and is not square, you will have to measure each room then add all the sq footage together.
Measure the length and the width of each floor of your home then multiply length X width for each floor total
Then add the totals of each floor together.
Example: 1st floor Length 50' Width 26',
50x26=1300 sq feet 1st floor
50x24=1200 sq feet 2nd floor
Add 1300+1200+2500 sq feet.