A square footage calculator finds the area of a room, floor, wall, or yard in square feet from simple measurements. Pick a shape — rectangle, circle, or triangle — enter the dimensions in feet, and get the area instantly, along with conversions to square yards, square meters, and acres.
Square footage drives most home-project math: flooring and carpet are quoted per square foot or square yard, paint coverage is rated in square feet per gallon, and real estate is priced and compared per square foot. Add an optional price per square foot to turn the measured area straight into a material cost estimate.
The Formulas: Rectangle, Circle, and Triangle
Each shape has a standard area formula, with all measurements in feet:
- Rectangle or square: Area = Length × Width
- Circle: Area = π × r², where r is the radius (half the diameter)
- Triangle: Area = ½ × Base × Height, where height is measured perpendicular to the base
Unit conversions from square feet: divide by 9 for square yards (carpet is often quoted this way), multiply by 0.0929 for square meters, and divide by 43,560 for acres.
If you measured in inches, divide each dimension by 12 before multiplying — or multiply the areas: a 30 in × 48 in tabletop is 2.5 ft × 4 ft = 10 sq ft.
How to Measure a Room (Including L-Shapes)
For a simple rectangular room, measure the length and width along the floor at the baseboards with a tape measure and multiply. Measure to the nearest half inch and round up slightly — coming up short on flooring is far worse than a little extra.
For an L-shaped or irregular room, split it into rectangles: measure each rectangular section separately, calculate each area, and add them. An L-shaped room made of a 12 × 10 ft section and a 6 × 8 ft section is 120 + 48 = 168 sq ft.
Buying materials, add a waste factor: 5%–10% extra for flooring and tile laid straight, and 15% for diagonal patterns, complex cuts, or natural stone. Closets and alcoves count too — walk the whole footprint.
Example: Flooring a 15 × 12 ft Living Room
A living room measures 15 ft long by 12 ft wide.
Area = 15 × 12 = 180 sq ft, which is 20 square yards or about 16.7 square meters.
With laminate flooring at $3.50 per square foot, the base material cost is 180 × $3.50 = $630. Adding a 10% waste factor means buying about 198 sq ft, or roughly $693 of material.
For paint, the relevant area is the walls: with 8 ft ceilings, the wall area is the perimeter (15 + 12 + 15 + 12 = 54 ft) × 8 = 432 sq ft. Since one gallon typically covers 350–400 sq ft per coat, two coats need about 2.5 gallons.
Frequently Asked Questions
How do I calculate square feet of a room?
Measure the room’s length and width in feet and multiply them together. A 15 ft by 12 ft room is 180 square feet. For irregular rooms, break the space into rectangles, calculate each area separately, and add them up. Measurements in inches should be divided by 12 first.
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. To convert square feet to square yards, divide by 9: a 180 sq ft room is 20 square yards. Carpet in the US is often priced per square yard, so this conversion comes up constantly.
How do I calculate the square footage of an L-shaped room?
Split the L into two rectangles, measure each one, and add the areas. For example, a main section of 12 × 10 ft (120 sq ft) plus an extension of 6 × 8 ft (48 sq ft) totals 168 sq ft. Any irregular straight-walled room can be handled this way by dividing it into rectangles.
How much extra flooring should I buy for waste?
Buy 5%–10% more than the measured square footage for standard straight installations, and about 15% extra for diagonal layouts, herringbone patterns, rooms with many corners, or natural materials with defects. The extra covers cutting waste, mistakes, and future repairs from the same dye lot.
Does square footage of a house include all rooms?
Listed square footage generally covers finished, heated, above-grade living space measured from the exterior walls. Garages, unfinished basements, attics, and open porches are usually excluded, though finished basements are often listed separately. Standards vary by region, so appraisals typically follow the ANSI Z765 standard.