Conversions & Core
Square Footage Calculator
Area of any room or surface in square feet, square yards and square metres — with waste allowance and material cost.
Inputs
Results
Adjust the inputs to see your result.
About this calculator
Almost every home project starts with one number: the area. This calculator finds it for rectangles, circles, triangles and trapezoids, converts it between square feet, square yards, square metres and acres, and can add a waste allowance and a price per square foot so the result is a buying figure, not just a measurement.
What this number means
Square footage is the two-dimensional area of a surface, measured in squares one foot by one foot. It is the unit almost every home material is priced and sold by in the US — flooring, tile, paint coverage, countertop fabrication and roofing all start here — so an area error of even 5% is a real money error once you multiply it by a material price.
The result above gives you more than the raw area. The buying quantity adds your waste allowance, because materials are cut to fit and some pieces are always lost to offcuts, breakages and pattern matching. The conversions let you compare products sold in different units: flooring in square yards, tile in square metres, land and large surfaces in acres.
The formula
Each shape has its own area formula. Dimensions are converted to feet first (inches ÷ 12, metres × 3.28084), then:
- Rectangle: Area = Length × Width
- Circle: Area = π × (Diameter ÷ 2)²
- Triangle: Area = ½ × Base × Height
- Trapezoid: Area = ½ × (Side A + Side B) × Height
Conversions from square feet: square yards = sq ft ÷ 9 · square metres = sq ft × 0.092903 · acres = sq ft ÷ 43,560.
Buying quantity = Area × (1 + waste %). Estimated material cost = buying quantity × price per square foot.
Worked example
Measuring a bedroom for flooring. The room is 12 ft long and 15 ft wide, measured inside wall to wall.
- Area = 12 × 15 = 180 sq ft
- In other units: 180 ÷ 9 = 20.0 sq yd · 180 × 0.092903 = 16.72 sq m
- Flooring needs a waste allowance. At 10%: 180 × 1.10 = 198 sq ft to buy
- At $3.25 per sq ft for laminate: 198 × $3.25 = $643.50 in materials
Set the calculator above to a rectangle, 12 × 15 ft, 10% waste and a $3.25 price and you will see exactly these numbers.
Assumptions and limitations
- Rectangles are assumed to have true 90° corners. Older homes often do not — measure both diagonals; if they differ, split the room into a rectangle plus a triangle and add the two areas.
- Irregular rooms (L-shapes, bays, alcoves) should be divided into simple shapes, calculated separately and totalled. A closet you plan to floor is its own small rectangle.
- Waste guidance: 5% for straight-lay plank flooring, 10% for tile and most installations, 15% for diagonal or herringbone layouts and roofs with many cuts. Paint and other liquids follow their own coverage rates, not area waste.
- The cost figure is materials only, at the price you enter. It excludes labour, underlayment, adhesives, trim, delivery and tax.
- Results are estimates for planning a purchase. For expensive materials, confirm with a second measurement before ordering — measure twice, buy once.
Frequently asked questions
Measure the length and width of the room in feet, inside wall to wall, and multiply them: a 12 ft by 15 ft room is 180 sq ft. For rooms that are not simple rectangles, split them into rectangles and triangles, calculate each piece, and add the results together.
Add 5% for straight-lay plank flooring, 10% for tile and most standard installations, and 15% for diagonal or herringbone patterns. Enter that percentage in the waste allowance field and the calculator shows the buying quantity directly.
Divide square feet by 9 for square yards, and multiply by 0.092903 for square metres. This calculator shows all three (plus acres) on every result, so you can compare products sold in different units.
Include any area the material will actually cover. If you are flooring the closet, measure it as its own small rectangle and add it. Exclude areas covered by fixed cabinetry or a bath/shower enclosure if the material will not go underneath them.
No. The cost line multiplies your buying quantity by the material price per square foot that you enter. Labour, underlayment, adhesives, trim, delivery and tax are separate and vary too much by region to estimate from area alone.