How to Calculate Square Footage: Rooms, Irregular Shapes, and Pro Tips

The Basic Square Footage Formula

Square Footage = Length (ft) × Width (ft)

For a room that's 12 feet long and 10 feet wide: 12 × 10 = 120 square feet (sq ft).

This works perfectly for rectangular rooms. Real-world spaces often require breaking areas into rectangles and adding them up — or handling circles, triangles, and irregular shapes.

Measuring a Rectangular Room

Step-by-Step

1. Measure the length of the room along the longest wall (in feet + inches)

2. Measure the width along the perpendicular wall

3. Convert inches to decimal feet: divide inches by 12 (e.g., 10'6" = 10.5 ft)

4. Multiply: L × W = square footage

Example: Room is 14'3" × 11'8"

• Length: 14 + 3/12 = 14.25 ft

• Width: 11 + 8/12 = 11.67 ft

• Area: 14.25 × 11.67 = 166.3 sq ft

Calculating Square Footage for Irregular Shapes

L-Shaped Rooms

Divide the L-shape into two rectangles, calculate each, and add:

Example: An L-shaped room with a main area of 15×12 and an alcove of 6×8:

• Rectangle 1: 15 × 12 = 180 sq ft

• Rectangle 2: 6 × 8 = 48 sq ft

• Total: 228 sq ft

Triangular Areas

Area = ½ × Base × Height

A triangular nook with a 6-foot base and 4-foot height: ½ × 6 × 4 = 12 sq ft

Circular Areas

Area = π × r² (where r = radius = diameter ÷ 2)

A circular room with a 14-foot diameter: π × 7² = 3.14159 × 49 = 153.9 sq ft

Rooms with Cutouts (Closets, Columns, Fireplaces)

Calculate the full rectangle, then subtract the cutout areas:

Room: 16 × 14 = 224 sq ft. Fireplace bump-out: 3 × 4 = 12 sq ft.

Usable floor area: 224 − 12 = 212 sq ft

Calculating Whole-House Square Footage

For real estate or insurance purposes, measure each room and sum them up. Include:

• All finished living spaces (bedrooms, living room, kitchen, bathrooms, hallways)

• Finished basements (counted separately in many markets)

• Closets and storage within the living area

Exclude:

• Garages

• Unfinished basements/attics

• Porches, patios, decks (outdoor spaces)

• Areas with ceiling height below 7 feet (varies by local standards)

Pro tip: Measure from the outside of exterior walls for total square footage (ANSI standard). Interior measurements undercount by 5-10% because they exclude wall thickness.

Square Footage for Common Projects

Flooring (Vinyl, Tile, Hardwood, Carpet)

Calculate room area, then add a waste factor:

• Tile: Add 10-15% for cuts and breakage

• Hardwood: Add 5-10% for cuts and defects

• Carpet: Add 10% (carpet comes in 12-foot rolls — seam placement matters)

Example: 200 sq ft room with tile: 200 × 1.10 = 220 sq ft of tile needed

Painting

Wall area (not floor area): Perimeter × Wall Height, minus door/window openings.

Room: 14 × 12, 8-foot ceilings, 2 windows (3×5 each), 1 door (3×7):

• Wall area: (14+12+14+12) × 8 = 416 sq ft

• Subtract openings: 2(3×5) + 1(3×7) = 30 + 21 = 51 sq ft

• Paintable area: 365 sq ft

• One gallon covers ~350 sq ft → need 2 gallons (1 gallon won't quite cover with 2 coats)

Roofing

Roofing uses the footprint area × a pitch factor. A 4/12 pitch multiplied by 1.054; a 6/12 pitch by 1.118; an 8/12 pitch by 1.202. Roofing materials are sold in "squares" (1 square = 100 sq ft).

Converting Square Footage

• Sq ft to sq meters: Multiply by 0.0929 (100 sq ft = 9.29 sq m)

• Sq ft to acres: Divide by 43,560 (1 acre = 43,560 sq ft)

• Sq ft to sq yards: Divide by 9 (1 sq yd = 9 sq ft)

Calculate Your Square Footage

Use our free Square Footage Calculator to quickly calculate the area of any room or space. Planning a flooring project? Try our Flooring Calculator for material quantities and cost estimates. For concrete work, see our Concrete Cost Calculator.

Frequently Asked Questions

What is the formula for square footage?

For a rectangle: Length × Width. For a triangle: ½ × Base × Height. For a circle: π × Radius². For irregular shapes, break them into standard shapes, calculate each, and add them together.

How do I measure square footage of a room with closets?

Measure the main room and the closet separately, then add them. Alternatively, measure the full room including the closet space if the closet shares walls with the room.

How many square feet in an acre?

One acre = 43,560 square feet. Visualize it as roughly 209 feet × 209 feet (though acres can be any shape).

Does square footage include walls?

For real estate listings (ANSI standard): yes, gross living area is measured from the outside of exterior walls. For flooring projects: no, measure the actual floor area inside the room.

How do I calculate square footage from inches?

Measure in inches, multiply Length × Width (both in inches), then divide by 144 (since 1 sq ft = 144 sq in). Example: 96" × 72" = 6,912 sq in ÷ 144 = 48 sq ft.