Square Footage Calculator is a free calculator and a set of plain guides for measuring area in square feet: rooms, floors, walls, roofs, houses and lots.
What the site does
The calculator on the home page takes feet and inches with fractions, works with four shapes, adds or subtracts areas and shows each step of the math. The guides explain the same math by hand, with worked examples, so any result can be checked on paper.
Where the numbers come from
Conversion factors come from NIST, the US measurement standards agency. Rules on what counts in a home's square footage come from the ANSI Z765 standard and Fannie Mae's selling guide. Material figures, such as paint coverage per gallon, come from the maker's own product pages and are named in the text. Each page links to its main sources.
How each page is checked
Every guide is researched from those sources first, then checked by a second reviewer against the same sources before it is published. Worked examples are recalculated, and every figure has to match the other pages on the site. The calculator runs the exact formulas the guides print.
What the site is not
Square Footage Calculator is not an appraiser, a builder or a government agency. The guides explain how area is measured; they are not legal, appraisal or building advice. Prices are not covered.
Corrections
If a number looks wrong, email admin@squarefootagecalculatr.com with the page and the figure, and it will be checked against the source and fixed.