Square Footage Calculators

AreaLab guides

Plain-language answers to square footage calculators questions, written from the same sourced data behind AreaLab. Every guide lists its sources and the date it was last updated.

• Updated June 10, 2026

  How do you calculate the square footage of a room?

  Multiply length by width in decimal feet — a 12 × 10 ft room is 120 square feet — and split irregular rooms into rectangles, triangles, and circles.

• Updated June 10, 2026

  How much paint do I need for a room?

  Wall area is perimeter × ceiling height: two coats on a 12 × 10 ft room at 350 sq ft per gallon is 3 gallons — or 2 after subtracting doors and windows.