How do I calculate the square feet of a room?

Measure the length and width of the room in feet along the longest walls and multiply them: a 12 ft × 14 ft room is 168 sq ft. If a measurement includes inches, divide the inches by 12 first (12 ft 6 in = 12.5 ft). For L-shaped or irregular rooms, split the floor into rectangles, calculate each one, and add them together — that is exactly what the multi-row calculator does.

What is the square footage of a 12x12 room?

A 12 ft × 12 ft room is 144 square feet (12 × 12 = 144). That equals 16 square yards (144 ÷ 9), which matters when carpet is priced per square yard.

How much extra flooring should I buy for waste?

Add 5–10% to your measured square footage for cuts, mistakes and future repairs — closer to 10% for small or cut-up rooms. For diagonal installations, herringbone or patterned tile, add 15%. Flooring is sold by the box, so round up to a whole box after adding the waste factor.

How many square feet are in an acre?

One acre is 43,560 square feet — roughly a 209 ft × 209 ft square, or about 75% of a football field. For land-sized conversions between acres, square feet and square meters, use the area calculator.

Is square footage measured from inside or outside the walls?

It depends on the purpose. For flooring, paint and rent comparisons, measure the interior wall-to-wall dimensions of each room. Real-estate listings in the US usually quote gross living area measured from the exterior walls, which runs larger — so your room-by-room total will normally be smaller than the listed square footage of the home.

Square Footage Calculator

Name: Square Footage Calculator
Author: Miikka

Measure any space room by room: add a row for each area, choose its shape (rectangle, L-shape, circle, triangle or trapezoid), and enter the dimensions in feet and inches. You get the square footage of every area plus a grand total in square feet, square yards and square meters — with a 10 % waste allowance for flooring and the total cost if you enter a price per square foot.

By Miikka · CalcBrew · Updated Sep 15, 2026

Shape

Length (ft)

(in)

Width (ft)

(in)

168 sq ft

Cost per sq ft ($, optional)

Total across 1 area

Square feet

168

+10 % waste: 185 sq ft

Square yards

18.7

Square meters

15.6

📌 Buying flooring? Add 5–10% to the total for cuts and waste — 15% for diagonal layouts or patterned tile.

How to measure a room

Measure wall to wall along the longest walls in feet and inches, and treat every alcove, closet or bay window as its own small rectangle. The formulas the calculator uses:

rectangle = length × width

L-shape = full length × full width − cut-out length × cut-out width

circle = π × (diameter ÷ 2)²

triangle = ½ × base × height

trapezoid = (side A + side B) ÷ 2 × height

Worked example — an L-shaped room: measure the full outer length and width as if the room were a complete rectangle, then the notch that is missing. A room 20 ft × 14 ft overall with an 8 ft × 6 ft corner cut out is 280 − 48 = 232 square feet. Choose “L-shape” in the calculator and type those four numbers, or split the floor into two rectangles (14 × 12 = 168 plus 8 × 8 = 64) — both give 232.

Inches convert as twelfths of a foot: 12 ft 6 in = 12.5 ft. The calculator handles this for you — just type feet and inches in their own boxes.

Square footage of common room sizes

Room	Sq ft	Sq yd (carpet)	+10 % waste	Flooring at $3.50/sq ft
10 × 10 bedroom	100	11.1	111	$389
10 × 12 bedroom	120	13.3	132	$462
12 × 12 bedroom	144	16	159	$557
12 × 14 living room	168	18.7	185	$648
15 × 20 living room	300	33.3	330	$1,155
20 × 20 two-car garage	400	44.4	441	$1,544
24 × 24 garage	576	64	634	$2,219
5 × 8 bathroom	40	4.4	44	$154
10 × 10 kitchen	100	11.1	111	$389

Conversions: 1 sq ft = 0.0929 m²; 1 sq yd = 9 sq ft; 1 acre = 43,560 sq ft. A typical US new home is about 2,300 sq ft; an average two-bedroom apartment 900–1,100 sq ft.

Common uses for square footage

Flooring: total the rooms, then add 5–10% for cuts and waste (15% for diagonal or patterned layouts) and round up to whole boxes.
Paint: wall area rather than floor area — measure each wall as a rectangle (width × height), then use the paint calculator to turn square feet into gallons.
Rent and real estate: divide monthly rent or sale price by square footage to compare homes fairly — $2,100 for 700 sq ft is $3.00/sq ft, while $2,400 for 900 sq ft is only $2.67.
Landscaping: square footage is the first step before volume — feed your total into the mulch calculator or cubic yard calculator to get cubic yards of material.

Frequently asked questions

Cite this calculator

APACalcBrew. (2026). Square Footage Calculator. https://calcbrew.com/square-footage-calculator

MLA“Square Footage Calculator.” CalcBrew, 2026, calcbrew.com/square-footage-calculator.

Link to https://calcbrew.com/square-footage-calculator. Results are estimates; cite the underlying formula or data source for academic work.

More in Home & Construction · All calculators

Square Footage Calculator

How to measure a room

Square footage of common room sizes

Common uses for square footage

Frequently asked questions

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