How do I calculate square footage?

What Is Square Footage?

Square footage is a measurement of area expressed in square feet. One square foot equals a square that is 12 inches (1 foot) on each side. It is the standard unit for measuring floor area, lot size, and material coverage in the United States and is used widely in real estate, construction, interior design, and home improvement.

When someone says a home is “1,500 square feet,” they mean the total livable floor area — the sum of all rooms, hallways, and closets — measures 1,500 sq ft. Understanding how to calculate square footage lets you estimate materials for projects, compare property sizes accurately, and plan room layouts with confidence.

How to Measure a Room

Accurate square footage starts with accurate measurements. Use a tape measure and measure along the floor from one wall to the opposite wall. Always measure at the longest and widest points, rounding to the nearest inch. For the most accurate results:

• Measure in feet and inches: Convert inches to decimal feet by dividing by 12. A room that is 12 feet 6 inches long is 12.5 feet.
• Measure from wall to wall: Include the space occupied by baseboards but exclude built-in furniture or appliances unless they are permanent.
• Measure twice: Small measurement errors compound when multiplied. A half-inch mistake on a 20-foot wall changes your total by almost a full square foot.

Calculating Irregular Shapes

Most rooms are not perfect rectangles. L-shaped rooms, rooms with alcoves, and open floor plans require a divide-and-conquer approach:

• Step 1: Sketch the room on paper and divide it into rectangles. An L-shaped room, for example, becomes two rectangles.
• Step 2: Measure and calculate the area of each rectangle separately.
• Step 3: Add the areas together for the total square footage.

For example, an L-shaped room might consist of a 10×15 section (150 sq ft) and an 8×10 section (80 sq ft), for a total of 230 square feet. If your room has a circular bay window or a triangular bump-out, calculate those areas with the appropriate formula (π × r² for circles, base × height ÷ 2 for triangles) and add them in.

Common Room Sizes

Knowing typical room sizes helps you sanity-check your measurements and estimate material needs before measuring:

• Small bedroom: 10×10 = 100 sq ft
• Standard bedroom: 12×12 = 144 sq ft
• Master bedroom: 14×16 = 224 sq ft
• Living room: 15×20 = 300 sq ft
• One-car garage: 12×20 = 240 sq ft
• Two-car garage: 20×20 = 400 sq ft

Converting Square Feet to Other Units

You will sometimes need to convert square footage into other area measurements for international projects, land purchases, or material specifications:

• Square feet to square meters: Divide by 10.764. Example: 1,200 sq ft ÷ 10.764 = 111.5 sq m.
• Square feet to square yards: Divide by 9. Example: 180 sq ft ÷ 9 = 20 sq yd (useful for carpet, which is often priced per square yard).
• Square feet to acres: Divide by 43,560. Example: 10,000 sq ft ÷ 43,560 = 0.23 acres.

Square Footage for Flooring

When buying flooring — hardwood, laminate, tile, or carpet — always order 10% more than your calculated square footage. This waste factor accounts for cuts at walls and doorways, pattern matching, and the occasional damaged piece. For diagonal installations or complex patterns, increase the waste factor to 15%.

For tile projects, the number of tiles depends on the tile size. A 12×12 inch tile covers exactly 1 square foot, so a 180 sq ft room needs 180 tiles (plus 10% waste = 198 tiles). A 6×6 inch tile covers 0.25 square feet, so you would need 720 tiles for the same room (plus waste). Always check the tile size and do the conversion before ordering.

Square Footage for Painting

Painting uses wall area, not floor area. To calculate wall square footage, multiply the perimeter of the room by the ceiling height. A 12×15 room with 8-foot ceilings has a perimeter of 54 feet, so the wall area is 54 × 8 = 432 square feet. Subtract roughly 20 square feet per door and 15 square feet per window. One gallon of paint covers approximately 350 square feet per coat, so this room would need about 1.2 gallons per coat — buy 2 gallons.

Common House Sizes by Square Footage

Average home sizes vary significantly by region and home type. Here are typical ranges in the US as of 2026:

• Studio apartment: 300–600 sq ft
• 1-bedroom apartment: 600–900 sq ft
• Small house (2-bedroom): 800–1,200 sq ft
• Average US home: 2,200–2,500 sq ft
• Large family home: 3,000–5,000 sq ft

Keep in mind that “square footage” in real estate listings typically refers to finished, livable space. Garages, unfinished basements, and attics are usually excluded from the listed square footage.