Square Footage & Room Area Calculator
Measure the area of a room, triangle or circle in feet and inches, decimal feet or metres. Add a waste margin, see square yards, square metres and acres, and total several rooms in a running ledger with an estimated material budget.
Written by Suhaib Hassan. Unit conversions follow NIST Special Publication 811. Our methodology.
It converts feet and inches to decimal feet, applies the shape formula, then adds your waste margin and converts to other units.
Flooring, paint and tile are all bought by area. One measurement here feeds every material estimate.
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Multi-room running ledger
Add rooms or zones from the form above to total several areas into one material list.
| Room | Dimensions | Net area | Margin | To buy | |
|---|---|---|---|---|---|
| Ledger total | — | — | |||
Room sizes and materials guide
Typical residential room sizes and the flooring, tile and paint they need. Each includes 10% waste. Paint assumes two coats at 350 sq ft per gallon, an 8 ft ceiling, one door (20 sq ft) and one window (15 sq ft).
| Space | Typical size | Area | 12×12 tiles | Flooring boxes | Paint (gal) |
|---|
Area formulas used
Rectangle
A = L × WTriangle
A = ½ × base × heightCircle
A = π × (diameter ÷ 2)²Feet and inches convert to decimal feet as ft + in ÷ 12. One square yard is 9 sq ft, one acre is 43,560 sq ft, and one square foot is 0.09290304 m².
Measuring a room
Measure wall to wall at the widest points. For an L-shaped room, split it into rectangles, add each to the ledger and read the total.
Leave out fixed cabinets or islands only if you will not floor under them. Add the waste margin last, not before.
Worked examples
Illustrative rooms, each checked by hand. The first is the default setup.
20 × 20 ft garage
10% waste.
× 1.10 = 440 sq ft
440 ÷ 9 = 48.89 sq yd
440 × 0.092903 = 40.88 m²
Feet and inches
A room 12 ft 6 in by 9 ft 3 in.
9 + 3/12 = 9.25 ft
12.5 × 9.25 = 115.63 sq ft
Round patio
A circle 12 ft across.
π × 6² = 113.10 sq ft
= 12.57 sq yd
How to calculate square footage
- Measure the length and width of the space in feet, or in feet and inches.
- Multiply length by width for a rectangle. Use the triangle or circle formula for other shapes.
- Split irregular rooms into simple shapes and add their areas.
- Add a waste margin before buying flooring, tile or other materials.
Square footage for listings can follow different rules than this simple floor area. For sales or rent, check the measurement standard your market uses.
By Suhaib Hassan · Reviewed 29 September 2026 · How CalculatePilot verifies formulas →
Sources
- NIST Special Publication 811, Guide for the Use of the International System of Units (SI), and NIST unit conversion factors for area.
Frequently asked questions
How do I calculate square feet from feet and inches?
Convert each side to decimal feet by dividing the inches by 12 and adding them to the feet, then multiply. A 12 ft 6 in by 9 ft 3 in room is 12.5 × 9.25 = 115.63 square feet.
How much waste should I add for flooring?
Five to 10% covers a simple rectangular room. Use about 15% for diagonal layouts, herringbone, or rooms with many angles or doorways.
What is the difference between square feet and linear feet?
Square feet measure area, length times width. Linear feet measure length only, for things such as baseboards or fencing. The Perimeter option shows the linear feet around a rectangular room.
How do I measure an L-shaped room?
Split the room into two rectangles, calculate each and add them. In this tool, add each rectangle to the ledger and read the total.
How many square feet are in a square yard?
There are 9 square feet in a square yard, because a yard is 3 feet and 3 × 3 = 9. Carpet is often sold by the square yard.
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