How to calculate square footage
For a rectangular space, multiply length × width (both in feet) to get square feet. A 12-foot × 15-foot room is 180 sq ft. If your measurements are in inches, divide by 12 first.
Rectangle: area = length × width
For irregular rooms, break the space into simple rectangles and triangles, calculate each, then add them together. Closets, bay windows, and bump-outs are usually handled as separate rectangles.
Formulas for each shape
Rectangle / Square
area = length × width
Most rooms. A 10×12 room = 120 sq ft.
Circle
area = π × r²
A 10-foot radius circle = 314 sq ft.
Triangle
area = ½ × base × height
A 10-foot base, 8-foot height triangle = 40 sq ft.
L-shape
area = (L₁×W₁) + (L₂×W₂)
Split into two rectangles, sum the areas.
Example room sizes
Some example dimensions and the area each gives. They are illustrations, not survey data or a building standard: real rooms vary widely, so measure yours.
| Room | Example size | Area |
|---|---|---|
| Bedroom | 12 × 12 ft | 144 sq ft |
| Larger bedroom | 14 × 20 ft | 280 sq ft |
| Living room | 15 × 20 ft | 300 sq ft |
| Kitchen | 10 × 16 ft | 160 sq ft |
| Dining room | 12 × 12.5 ft | 150 sq ft |
| Full bathroom | 8 × 10 ft | 80 sq ft |
| Half bath | 5 × 5 ft | 25 sq ft |
| Home office | 10 × 12 ft | 120 sq ft |
| One-car garage | 12 × 20 ft | 240 sq ft |
| Two-car garage | 20 × 24 ft | 480 sq ft |
How to measure a room
- Measure wall-to-wall at the baseboards, don't include the baseboard itself, and skip any built-in cabinets or fixtures.
- Use a laser measure if you have one. A 25-foot tape measure works for most rooms if you're careful to keep it taut and straight.
- Record in inches for accuracy, then convert to feet at the end. "11 feet 8 inches" is more precise than "about 12 feet."
- Handle closets separately, calculate closet floor area and add to the main room, or keep separate if closets don't need the same treatment.
- For irregular shapes, break the floor into rectangles you can measure. Add the areas. For curves, approximate with triangles or quarter-circles.
Flooring, painting, and landscaping
Flooring
Floor area plus an allowance for offcuts. The allowance is a rule of thumb rather than a standard, and it grows for diagonal lays and rooms with many corners. Flooring is sold in whole boxes, so round up.
Painting
Paint needs wall area rather than floor area: perimeter × ceiling height, less openings. The paint calculator allows 20 sq ft for a typical door and 15 for a window, and starts at 350 sq ft per gallon per coat, a typical label figure. The spread rate printed on your can governs.
Landscaping / sod
Measure the yard in sq ft, then divide by what the supplier says one pallet of sod or one bag of seed covers. Pallet sizes and seeding rates vary by supplier and grass type, so use the figures on the label or quote.
Unit conversion reference
| From | To | Multiply by |
|---|---|---|
| Square meters | Square feet | × 10.764 |
| Square feet | Square meters | × 0.0929 |
| Square yards | Square feet | × 9 |
| Square feet | Square yards | × 0.1111 |
| Acres | Square feet | × 43,560 |
| Square feet | Acres | ÷ 43,560 |
From NIST's exact definitions: 1 foot = 0.3048 metre, 1 square yard = 9 square feet, 1 acre = 43,560 square feet. The metric factors are rounded.
Frequently asked questions
How do I calculate square feet of a room?
Take the two wall-to-wall measurements in feet and multiply them. Say the room runs 12 by 15 feet: 12 × 15 = 180 square feet. If you measured in inches, convert first, since 12 inches make a foot (144 inches is 12 feet). The calculator above does the unit conversion for you and also handles circles, triangles and two-part L-shapes.
How many square feet is a 12x12 room?
It is 144 square feet, because 12 × 12 = 144. Nearby sizes for comparison: 10×10 = 100 sq ft, 10×12 = 120 sq ft, 12×14 = 168 sq ft, 12×15 = 180 sq ft, 14×16 = 224 sq ft. If you are buying flooring for it, allow extra for cuts; with a 10% allowance, a common rule of thumb rather than a standard, that comes to 158.4 sq ft.
How do I calculate square feet from inches?
Either convert each side to feet and multiply, or multiply the inches and divide by 144, the number of square inches in a square foot (12 × 12). A 144 by 96 inch floor is 12 ft × 8 ft = 96 sq ft; the other route gives 13,824 square inches ÷ 144 = 96 sq ft. Pick "inches" in the unit menu and the calculator converts for you.
How many square feet in an acre?
An acre is exactly 43,560 square feet, by NIST's definition. So a quarter acre is 10,890 sq ft, half an acre 21,780 sq ft and 5 acres 217,800 sq ft. As a square, an acre is about 208.7 feet on each side. The old surveyors' shape is one chain (66 ft) by one furlong (660 ft), and 66 × 660 = 43,560.
How do I calculate square footage of an odd-shaped room?
Sketch the floor and cut it into pieces you can measure: rectangles, right triangles, the odd half-circle. Work out each piece on its own and add them; if a piece is a notch taken out of a bigger rectangle, subtract it instead. Two-rectangle rooms fit the L-shape tab directly. For anything with more parts, run each piece through the calculator and total the answers.
How do I calculate sq ft for flooring?
Start from the floor area, then add a cutting allowance. Around 10% is the usual rule of thumb (less for a plain rectangle, more for a room full of angles), but it is a convention, not a standard. At 10%, a 200 sq ft room means ordering 220 sq ft. Buy in whole boxes, and leave out areas under fixed cabinets. The flooring calculator does the box count.
What is the square footage of a circle?
Use π × r², where r is the radius. A round patio 10 feet from centre to edge covers π × 10² = 314.16 sq ft. With a diameter, halve it first: a 20-foot-wide circle has that same 10-foot radius, so it also comes to 314.16 sq ft.
How do I convert square meters to square feet?
A foot is exactly 0.3048 metre, so one square metre is 1 ÷ 0.3048² ≈ 10.764 sq ft. A 100 square metre flat is about 1,076 sq ft. Other sizes: 50 sq m = 538 sq ft, 75 sq m = 807 sq ft, 150 sq m = 1,615 sq ft, 200 sq m = 2,153 sq ft. To go back, multiply square feet by 0.0929.
How many square feet do I need for paint?
Paint goes on the walls, so the number you want is wall area: the room's perimeter times its height, less the doors and windows. Take a 12 by 15 foot room with 8-foot walls: 54 ft × 8 = 432 sq ft. Taking off one door and two windows at typical sizes (20 and 15 sq ft) leaves 382 sq ft. Two coats at 350 sq ft per gallon, a typical label figure, is 2.18 gallons, so buy 2.5. The paint calculator works this out for you.
How do I measure square footage for rent?
There is no single rule. Listings and leases may count the whole enclosed area, including interior walls and closets, or only usable floor, and they usually list garages, balconies and patios apart from the main figure. For a condo or apartment, shared hallways and lobbies are normally left out. If the number matters to a rent or price, ask which measurement standard the landlord or listing used.