Home Square Footage Calculator

The formula

total = length × width × storeys + garage + unfinished basement

Each floor is the footprint, 30 × 25 = 750 sq ft, repeated for the number of storeys. Garage and unfinished basement are added as flat areas because they sit outside the stacked footprint. Finished area is the footprint times storeys only — the spaces you would heat and furnish.

Worked examples

30 × 25 ft, two storeys, 400 sq ft garage → 1,900 sq ft total, 1,500 finished
15 × 25 ft footprint → 1,150 total, 750 finished
60 × 25 ft footprint → 3,400 total, 3,000 finished
One storey instead of two → 1,150 total, 750 finished
Four storeys → 3,400 total, 3,000 finished
Garage of 200 sq ft → 1,700 total
10 sq ft of unfinished basement → 1,910 total

Storeys multiply the footprint, while garage and basement add to it once. That is why a two-storey house with the same plot as a bungalow is nearly twice the size, and why a big garage can quietly add a fifth of the total.

Which number to quote

Listings quote finished, above-grade living area. An appraiser measuring to ANSI standards excludes the garage entirely and treats a finished basement as a separate line, so a house advertised at 1,500 sq ft with a 400 sq ft garage is not a 1,900 sq ft house for lending purposes.

That also means the valuation line in the tool is generous: it applies $200 to the total including garage and unfinished space. On the defaults, valuing only the finished 1,500 sq ft gives $300,000, which is closer to how a price per square foot is normally quoted.

Measuring properly

Measure the outside of the heated envelope, not individual rooms: internal walls and stairwells are part of the floor area, and room-by-room totals come out low. Bay windows, dormers and any floor with a low sloped ceiling are counted by rule, usually only the portion above a minimum head height, so a loft conversion rarely adds its full footprint.

For a quick check, compare your total with the county assessor’s record. A large difference is usually a converted garage, an enclosed porch or an unpermitted addition, and any of those matters when you sell.

Frequently Asked Questions