How to calculate square footage for any home project

Square footage is the language of real estate and home improvement. Whether you are buying flooring, ordering paint, or estimating landscaping materials, everything starts with the same basic calculation. Here is how to measure and calculate square footage for any project.

The basic formula

For a rectangular room, multiply the length by the width. A room that is 12 feet long and 10 feet wide is 120 square feet. This works for any rectangle — rooms, lots, countertops, and walls.

Always measure in feet. If your tape measure shows inches, divide by 12 to convert. A wall that is 8 feet 6 inches long is 8.5 feet. Multiply by the height to get square footage.

Handling irregular shapes

Not every space is a neat rectangle. For L-shaped rooms, divide the space into two rectangles, calculate each one, and add them together. For a room that is 20 by 12 with a 5 by 5 alcove, you get 240 plus 25 for a total of 265 square feet.

For triangular spaces, multiply the base by the height and divide by two. A triangular garden bed with a 10-foot base and 6-foot height is 30 square feet.

For circles, use the formula πr². A circular patio with a 10-foot radius (20-foot diameter) is 3.14 times 100, or 314 square feet.

Accounting for waste

When buying materials, never order exactly the square footage of your space. Flooring typically needs 10 percent extra for cuts and mistakes. Tile projects often require 15 percent because of breakage and complex cuts. Paint usually calls for a 5 percent buffer.

Ordering extra costs a little more upfront but prevents the nightmare of running out of material mid-project. The Square Footage Calculator includes waste percentage in its estimates so you order the right amount.

Measuring complex areas

Stairs involve measuring the tread (the part you step on) and the riser (the vertical part). For each step, multiply tread depth by width for the tread area, then riser height by width for the riser area. Add them together and multiply by the number of steps.

Walls with windows and doors: Calculate the total wall area, then subtract the square footage of each opening. A standard door is roughly 21 square feet. A 3-by-5-foot window is 15 square feet. Subtract these from your total.

Converting between units

Sometimes you will encounter dimensions in yards or meters. One square yard equals 9 square feet. One square meter equals about 10.76 square feet. For landscaping materials sold by the cubic yard, you need to multiply square footage by depth in feet and divide by 27.

Common project estimates

• A standard 10-by-12-foot bedroom is 120 square feet
• A 20-by-30-foot living room is 600 square feet
• A 500-square-foot deck at 200 square feet for materials means 40 percent waste for diagonal patterns
• A 2,000-square-foot house has roughly 3,200 square feet of wall area (assuming 8-foot ceilings)

Accurate square footage saves money and materials. Whether you are laying tile or seeding a lawn, measuring carefully and using the Square Footage Calculator ensures you buy the right amount and avoid costly returns or shortages.