How to Calculate Square Footage of a Room (Any Shape)

The exact formulas for calculating square footage of rectangular, L-shaped, circular, and triangular rooms, with worked examples for each.

Every room shape reduces to a small handful of formulas — the trick is picking the right one and measuring the right dimension, not the math itself.

Rectangle: the baseline

Square footage = length × width, both measured in feet. A 12 ft × 10 ft room is 12 × 10 = 120 sq ft.

L-shaped room

Measure the room as one large outer rectangle, then measure the rectangular notch missing from a corner. Subtract the notch: (outer length × outer width) − (cutout length × cutout width). A 16×12 ft room missing a 5×4 ft corner is (16×12) − (5×4) = 192 − 20 = 172 sq ft.

Circular room or area

Area = π × radius². Measuring diameter (straight across) is usually easier than radius — just divide by 2 first. A 12 ft diameter circle has a 6 ft radius: π × 6² ≈ 113.1 sq ft.

Triangular area

Area = (base × height) ÷ 2, where height is measured perpendicular to the base, not along a slanted side. A 10 ft base with a 6 ft height is (10×6) ÷ 2 = 30 sq ft.

Multiple rooms at once

Calculate each room separately with its matching formula, then add the results together for a whole-floor or whole-house total.

Calculate any of these shapes — including several rooms totaled together — in the Square Footage / Area Calculator.