How to Measure Square Footage for Any Project
Square footage is the starting number for almost every material estimate. This guide shows how to measure rectangles, triangles, circles, and irregular rooms — and convert between units.
Ready to run the numbers? Use our Square Footage Calculator or the Flooring Calculator to get an instant material estimate.
Rectangles: the basic formula
For any rectangular room, lot, or area, multiply length × width in feet. Measure to the nearest inch and convert inches to feet (divide by 12) before multiplying. This single formula covers most home projects.
Source: Standard rectangle area. Convert inches to feet by dividing by 12.
A 15×20 ft living room = 300 ft². A 12 ft 6 in × 10 ft wall = 12.5 × 10 = 125 ft².
Triangles and circles
For a triangular area — a corner of a yard or a gable end — use base × height ÷ 2. For a circular area like a round patio or tree ring, use π × (diameter ÷ 2)².
Source: Standard area formulas. π ≈ 3.14159.
A gable 16 ft wide and 5 ft tall: (16 × 5) ÷ 2 = 40 ft². A 10 ft diameter round patio: π × 5² = 78.5 ft².
L-shaped and irregular rooms
Break an irregular shape into simple rectangles and triangles, measure each one, and add the areas. For an L-shaped room, split it into two rectangles at the inside corner. Sketch the shape first so you do not double-count or miss a section.
Conversions you will use
- 1 square yard = 9 square feet (carpet is sold by the yard).
- 1 square meter ≈ 10.764 square feet.
- 1 acre = 43,560 square feet.
- 1 cubic yard = 27 cubic feet (for concrete, mulch, gravel).
Once you have square footage, plug it into the relevant material calculator to get bags, boxes, gallons, or yards. Measuring accurately up front is what keeps every downstream estimate honest.
Frequently asked questions
How do I calculate square footage of a room?
Multiply length × width in feet. For a 12×12 ft room that is 144 ft². Convert any inches to feet first (divide by 12), then multiply.
How do I measure square footage of an L-shaped room?
Split the room into two rectangles at the inside corner, calculate each area (length × width), and add them. The same break-it-up approach works for any irregular shape.
How many square feet are in a square yard?
One square yard equals 9 square feet. Carpet and some flooring are priced by the square yard, so divide your square footage by 9 to compare prices.
Calculators for this guide
Put these numbers to work with the free calculators referenced above.