How to Calculate Square Feet — Formulas for Any Shape

Square footage = length × width, in feet. That’s the foundational formula. Whether you’re measuring a bedroom, calculating tile coverage, estimating a yard, or pricing a real estate listing — the math comes back to that one equation.

Here’s how to apply it to any room or shape, plus tips for irregular spaces.

The basic formula: rectangle

Square feet = Length (ft) × Width (ft)

Most rooms are rectangles. Measure the length and width in feet (use a tape measure or laser distance tool), then multiply.

Example: A bedroom is 12 feet long and 10 feet wide.

Square feet = 12 × 10 = 120 sq ft

If your measurements are in inches, divide by 12 first to convert to feet. If they’re in meters, multiply by 10.764 to convert.

Square shape formula

For a square room (all sides equal):

Square feet = side × side, or side²

Example: 8-foot × 8-foot square space.

Square feet = 8² = 64 sq ft

Circle formula

Square feet of a circle = π × r²

Where r is the radius (half the diameter) in feet.

Example: A round outdoor patio with 12-foot diameter (6-foot radius).

Square feet = 3.14159 × 6² = 3.14159 × 36 = 113.1 sq ft

For a half-circle: divide the full circle by 2.

Triangle formula

Square feet = (Base × Height) / 2

For a right triangle, the base and height are the two perpendicular sides.

Example: Triangular garden bed with a 10-foot base and 6-foot height.

Square feet = (10 × 6) / 2 = 30 sq ft

For a non-right triangle, use the formula with the perpendicular height (drop a vertical line from the apex to the base).

L-shaped room

L-shaped rooms (common in older homes) are two rectangles joined at a right angle.

Method: Split the L into two rectangles, calculate each, then add them.

Example:

Rectangle A: 14 ft × 10 ft = 140 sq ft (main room)
Rectangle B: 6 ft × 8 ft = 48 sq ft (alcove)
Total: 140 + 48 = 188 sq ft

Irregular shapes

For unusual shapes, the best approach is to break them into smaller rectangles and triangles, calculate each, then add them all.

Example: A trapezoidal room with parallel sides of 14 ft and 10 ft, and 12 ft between them.

Trapezoid formula: ((side1 + side2) / 2) × height
((14 + 10) / 2) × 12 = 12 × 12 = 144 sq ft

Or split it into a rectangle (10 × 12 = 120) plus a triangle ((14-10) × 12 / 2 = 24).

Total: 120 + 24 = 144 sq ft (same answer)

Common applications

Real estate listings

Property listings show “total square footage” which usually means the sum of all heated/finished living space. Excludes: garages, unfinished basements, decks, porches. Includes: bedrooms, bathrooms, hallways, closets, stairwells (counted on each level).

Flooring / carpet / tile

Square footage tells you how much material to buy. Always add 10-15% for waste. For odd-shaped rooms or complex patterns, add 20%. Buy in same dye lot (carpets) or same production run (tile) to ensure color matches.

Painting

Average gallon of paint covers 350-400 sq ft of wall. To calculate wall area: perimeter (sum of all wall lengths) × ceiling height − doors and windows. Subtract about 20 sq ft per standard door, 15 sq ft per standard window.

Lawn / yard / landscaping

Lawn fertilizer, weed killer, and seed are sold by square footage. Measure your yard with the same length × width formula. For irregular yards, divide into rectangles or use online satellite-measurement tools.

Solar panels

Solar panel placement requires knowing roof square footage. The usable area is typically 60-80% of total roof (subtract roof obstructions, vents, chimneys, dormers).

Square feet vs square inches vs square yards

Conversion factors:

To convert	Multiply by
Square inches → square feet	/ 144
Square yards → square feet	× 9
Square meters → square feet	× 10.764
Acres → square feet	× 43,560

Example: A 6 × 8 ft area = 48 sq ft = 6,912 sq inches = 5.33 sq yards = 4.46 sq meters.

Common room sizes (reference)

Room	Typical sq ft
Closet (walk-in)	25-50
Small bathroom	35-50
Standard bathroom	50-100
Bedroom (small)	100-150
Bedroom (master)	200-300
Living room	200-400
Kitchen (small/galley)	100-150
Kitchen (eat-in)	200-300
Garage (2-car)	400-500
Average US home	2,300
Apartment (studio)	400-600
Apartment (1BR)	650-900
Apartment (2BR)	900-1,300

Measurement tips

Use a laser distance tool for accuracy on rooms over 12 feet. Tape measures get inaccurate at long distances due to sag.
Measure twice — once each direction. Square them off (90° corners) for accuracy.
Round up when measuring for material purchase. Always have extra rather than running out.
Document at the same wall height — most rooms have slightly different measurements at floor vs ceiling due to wall thickness. Use floor measurement for square footage.
For floor plans, sketch the room and note each measurement. Reference photos help when you’re back at the store.

When NOT to use simple square footage

Vaulted ceilings: Square footage doesn’t capture vertical volume (use cubic feet for HVAC/painting tall ceilings).
Multi-story homes: Each level has its own square footage. Total = sum of all levels.
Outdoor areas vs indoor: Real estate usually counts only indoor heated space. Decks, patios, and lanais are often listed separately.
Wall area vs floor area: For painting, you need wall area (perimeter × height − openings). For flooring, you need floor area.

Frequently asked questions

Q: How many square feet in a 10x12 room? A: 10 × 12 = 120 sq ft.

Q: How do I measure square footage for carpet? A: Measure length × width of each room you’ll carpet. Add the rooms together. Add 10-15% for waste. Order in linear yards (1 yard = 3 feet wide; if your carpet is 12 ft wide, divide sq ft by 12 to get linear yards).

Q: How many square feet is an acre? A: 1 acre = 43,560 square feet. A football field (including end zones) is about 57,600 sq ft (about 1.32 acres).

Q: What’s the average square footage of a US home? A: Around 2,300 sq ft as of 2024. This has grown from ~1,500 sq ft in 1973. Median new-construction home is about 2,200 sq ft.

Q: How do I calculate square feet of a wall (for painting)? A: Length of wall × ceiling height. Then subtract about 20 sq ft per standard door and 15 sq ft per window.

Q: Can I measure square footage with my phone? A: Apps like MagicPlan, RoomScan, and the iPhone’s built-in Measure app use augmented reality to estimate room dimensions. Accuracy: 2-5% off vs tape measure for typical rooms. Good for quick estimates, not final purchase decisions.

Square Footage Calculator — Quick calculation for any shape
Cubic Yard Calculator — Volume for concrete, mulch, gravel
Paint Calculator — Gallons needed for walls
Flooring Calculator — Carpet, tile, hardwood quantities
Roofing Calculator — Roof area calculations
Asphalt Calculator — Driveway tonnage

Square footage is one of those fundamental calculations you’ll use throughout life — from buying carpet to selling a house. Master the rectangle formula, then learn to break complex shapes into simple parts.