How to Calculate Square Footage: Rooms, Walls and Cutouts

For a rectangle, square footage = length in feet × width in feet. A 14 ft 6 in × 11 ft 3 in room is 163.125 sq ft because 14.5 × 11.25 = 163.125. For an L-shaped room, calculate non-overlapping rectangles and add them, or subtract a rectangular cutout.

Square feet measure a surface. Concrete and other fill materials also need depth before you can calculate volume.

First convert feet and inches

Divide inches by 12, then add the whole feet. For the example room:

• 14 + 6 ÷ 12 = 14.5 ft.
• 11 + 3 ÷ 12 = 11.25 ft.
• 14.5 × 11.25 = 163.125 sq ft.

Use the feet-and-inches guide for fractional inches. Do not enter 14.6 feet for 14 ft 6 in.

Worked example: an L-shaped floor

Suppose the outer rectangle measures 20 ft × 15 ft, with a 6 ft × 5 ft corner missing.

Draw and label the cutout before measuring. If instead you split the L into two rectangles, make sure they do not overlap; both methods should give 270 sq ft.

For a triangular section, use base × perpendicular height ÷ 2. A 12 ft base and a 5 ft perpendicular height give 30 sq ft. The sloping side is not the perpendicular height.

From measured area to a material order

Assume the floor above needs an example 10% cutting allowance, and the selected flooring carton states 23.5 sq ft coverage:

1. Area with allowance: 270 × 1.10 = 297 sq ft.
2. Exact cartons: 297 ÷ 23.5 = 12.638….
3. Round up to 13 cartons, covering 13 × 23.5 = 305.5 sq ft.

Both the allowance and carton coverage are example inputs, not universal recommendations. Pattern, cuts, repair stock and the actual product determine the order. Do not add the same allowance again after rounding to cartons.

Walls and openings

A 16 ft × 8 ft wall has 128 sq ft of gross area. Subtract an unpainted 3 ft × 7 ft doorway and a 4 ft × 3 ft window: 128 − 21 − 12 = 95 sq ft.

Record which openings were deducted, and measure any reveals or returns separately. Use the US paint calculator for a paint estimate with wall dimensions, openings, coats and coverage. Paint coverage per gallon is not the same as floor area per carton.

Convert square feet to other area units

Divide square feet by 9 for square yards. Multiply square feet by 0.09290304 for square meters. Thus 270 sq ft = 30 sq yd, or about 25.08 m².

In the US unit converter, choose Area, select the source and destination units, and enter the calculated area. It converts an area you already know; it does not measure a room or multiply its dimensions for you.

When you need cubic yards instead

Multiply square feet by depth in feet, then divide by 27. The 270 sq ft floor at a specified example depth of 4 in would contain 270 × (4 ÷ 12) ÷ 27 = 3.333… yd³ before allowance. See the concrete cubic-yard calculation.

These are construction takeoff methods, not a standard for reporting real-estate living area or a structural design. NIST's unit tables supply the unit relationships; project measurements and product coverage supply the estimating inputs.