Square footage calculator for rooms, floors and any shape

How to use it

Pick the unit and the shape. Choose the unit you measured in (feet, inches, meters or centimeters) and the shape closest to the surface. For a room made of several parts, switch to Several rooms.
Enter the measurements. Type the lengths shown under the drawing. The area appears as you type, in both square feet and square meters, and the drawing redraws to scale.
Add waste and price. To buy materials, set the extra for waste (10% is common for flooring laid straight) and, if you want, the price per square foot. You get the quantity to order and the estimated cost.

Area formulas for every shape

Area measures the surface inside a shape, in square units. A square foot is a square with 1 ft sides; a square meter one with 1 m sides. Each formula below takes lengths in the same unit and gives the area in that unit squared.

Shape	Formula	Example
Rectangle	length × width	12 × 10 ft = 120 sq ft
Circle	π × radius²	radius 6 ft = 113.1 sq ft
Triangle	base × height ÷ 2	24 × 8 ft = 96 sq ft
Triangle, three sides	√(s(s−a)(s−b)(s−c)), s = half perimeter	50, 60, 70 ft = 1,469.69 sq ft
Trapezoid	(base 1 + base 2) ÷ 2 × height	16, 10 and 9 ft = 117 sq ft
Ring	π × (outer² − inner²)	8 and 5 ft = 122.52 sq ft

The three-side triangle uses Heron's formula, described by Heron of Alexandria in his Metrica in the first century. It is handy for lots and gardens where you can measure the sides but not the height. The tool uses the numerically stable version recommended by William Kahan, which stays accurate even for very thin triangles.

The height of a triangle or trapezoid is the perpendicular distance between base and top, not the length of a slanted side. Using the slanted side overestimates the area.

Square feet and square meters

One foot is exactly 0.3048 m, so one square foot is 0.3048² = 0.09290304 m², exactly. Going the other way, one square meter is about 10.76 sq ft. A quick mental rule: multiply square meters by 10 and add 7.6% to get square feet.

Do not convert linear and square units with the same factor. A room 10 ft long is 3.048 m long, but 100 sq ft are only 9.29 m², not 30.48. If you measured in inches, the tool converts each side before multiplying, so you never mix units by mistake. To convert single lengths, such as a wall in inches, use the cm to inches converter.

Worked examples

An L-shaped living room

Split the L into two rectangles: 20 × 12 ft and 10 × 8 ft. 240 + 80 = 320 sq ft (29.73 m²). In the tool, enter one rectangle per row in Several rooms.

Flooring with 10% waste

For those 320 sq ft, add 10%: 320 × 1.10 = 352 sq ft to buy, 32 of them for cuts. At $4.50 per sq ft the material costs $1,584.

A room measured in meters

A 5 × 4 m room is 20 m², which is 215.28 sq ft.

A round patio

A circular patio 12 ft across has a radius of 6 ft: π × 6² = 113.1 sq ft.

Measuring tips and waste allowance

Measure wall to wall at floor level, at the widest points. Rooms are rarely perfectly square, so measure each side twice and use the larger value.
Split odd shapes into simple ones: rectangles for the main parts, triangles for angled corners, then add them up. Subtract fixed islands or fireplaces if no flooring goes under them.
Waste depends on the pattern: around 10% for planks or tiles laid straight, 15% or more for diagonal or herringbone patterns and for rooms with many corners.
Round up to whole boxes: flooring is sold by the box or pack; divide the quantity by the coverage on the box and round up.
For paint, the area of a wall is its width times the ceiling height, minus doors and windows. Check the coverage per gallon or liter on the can.

If prices include sales tax or VAT and you need the net amount, the VAT calculator separates it. To compare two quotes, the percentage calculator shows the difference in percent.

Sources

NIST Special Publication 811 (2008), Appendix B.8: 1 ft² = 9.290304 × 10⁻² m² (exact). Checked 14/10/2026.
NIST, “SI Units – Length”: international foot of exactly 0.3048 m, adopted on 1 July 1959. Checked 14/10/2026.
Heron of Alexandria, Metrica (1st century AD), Book I: area of a triangle from its three sides.
W. Kahan, “Miscalculating Area and Angles of a Needle-like Triangle” (2014): numerically stable form of Heron's formula. Checked 14/10/2026.

The examples on this page are computed with the same code as the calculator, so the numbers in the text always match the tool.

Frequently asked questions

How do I calculate square footage?

Multiply the length by the width, both in feet. A 12 × 10 ft room is 120 sq ft. For other shapes use the formulas in the table above or pick the shape in the calculator.

How do I calculate the square footage of an L-shaped room?

Divide it into two rectangles, calculate each one and add them. 20 × 12 ft plus 10 × 8 ft is 320 sq ft.

How many square feet are in a square meter?

About 10.76. One square foot is exactly 0.09290304 m².

How much extra flooring should I buy?

Usually 10% more than the floor area for a straight layout, and 15% or more for diagonal or herringbone patterns. Keep a few spare pieces for future repairs.

How do I calculate square footage from inches?

Either convert each side to feet first (divide by 12) and multiply, or multiply the inches and divide by 144, because a square foot is 12 × 12 = 144 square inches. The calculator does this for you if you choose inches.

How do I find the area of a triangle without the height?

If you know the three sides, use Heron's formula: take half the perimeter s, then the area is the square root of s(s−a)(s−b)(s−c). Choose Triangle (three sides) in the calculator.

Do I include closets and hallways?

For flooring, include every part that gets the same floor, closets included. For real estate listings the rules depend on the country and the standard used, so check the local definition.

Last updated Wednesday, October 14, 2026

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