Square Footage Calculator
Area and perimeter for the five shapes that cover almost every takeoff — rectangles, triangles, circles, trapezoids, and rings — plus a multi-room adder to total a whole floor. Results convert to square yards for flooring and other materials sold by the yard. All dimensions in feet. Free, no login.
Single Area
Multi-Room Total
Area
Enter dimensions to calculate
How this calculator works
This is pure plane geometry — no code table, no citation needed. Each shape is one closed-form formula, and irregular floors are handled the way estimators actually do it: split the plan into rectangles (and the odd triangle), compute each, and add them up. The only conversion in play is the fixed one:
area (ft²) = shape formula · 1 sq yd = 9 sq ft · sq yd = ft² ÷ 9
Perimeter comes along free for rectangles (2 × (L + W)) and circles (π × diameter) — useful for baseboard, edge forms, and fencing. Note the calculator takes diameter for circles and rings, not radius, because that is what a tape measure gives you across a slab or tank pad.
Worked example
A 24 × 18 ft great room getting new flooring:
- Area: 24 × 18 = 432 sq ft.
- Square yards: 432 ÷ 9 = 48 sq yd — the number a carpet supplier quotes against.
- Perimeter: 2 × (24 + 18) = 84 lin ft of baseboard or transition.
Enter the same room above (Rectangle, 24 × 18) to reproduce it, then use the multi-room adder to stack the rest of the floor — an L-shaped plan is just two rectangles.
Reference: shape formulas
Every shape the calculator supports, with a sample computed by the same engine.
| Shape | Formula | Example | Area |
|---|---|---|---|
| Rectangle | L × W | 24 × 18 ft | 432 sq ft |
| Triangle | ½ × base × height | 30 × 14 ft | 210 sq ft |
| Circle | π r² (enter diameter) | 12 ft dia | 113.1 sq ft |
| Trapezoid | (a + b) ÷ 2 × height | 20 & 12 ft sides, 10 ft deep | 160 sq ft |
| Ring (annulus) | π (R² − r²) (enter diameters) | 12 ft outer, 6 ft inner | 84.82 sq ft |
Frequently asked questions
How do I calculate the square footage of a room?
Length × width, both in feet: a 12 × 15 room is 180 ft². Measure wall-to-wall at floor level, and for anything that is not a clean rectangle, split the space into rectangles and triangles and add the pieces — the multi-room adder totals the rectangular sections for you, and the shape selector handles triangles and the rest.
How do I convert square feet to square yards?
Divide by 9, since a square yard is 3 ft × 3 ft: 180 ft² is 20 yd². Carpet and some sheet goods are still quoted per square yard, so the calculator shows both figures on every result.
How do I figure the square footage of an L-shaped or odd room?
Break it into simple shapes and total them. An L-shape is two rectangles; a bay or splayed wall is a trapezoid; a clipped corner is a triangle (base × height ÷ 2). Compute each piece with the shape selector, or enter the rectangles in the multi-room list and the calculator keeps a running total in square feet and square yards.
Do I enter radius or diameter for a circle?
Diameter — the full width across the circle. The tool computes area as π × (d ÷ 2)² and also returns the circumference as the perimeter, which is what you need for edge forms or band material. The annulus (ring) shape works the same way from the outer and inner diameters — useful for a ring of paving or rock around a tank or tree.
How much extra should I add for flooring waste?
This calculator gives net area — it adds no waste. Typical allowances run about 5–10% for straight-lay plank or tile in simple rooms, and more for diagonal layouts, pattern-matched material, and rooms with a lot of cuts; those are rules of thumb, not guarantees. Figure your net area here, then apply the waste factor your material and layout warrant.
Method: plane geometry with a fixed 9 sq ft per sq yd conversion — there is no code or standard behind an area number, only the measurements you feed it. Field areas differ from plan areas: measure to the surfaces you will actually cover, deduct large openings where the material stops (stairwells, islands), and remember that material orders add a waste factor on top of net area — that allowance belongs in the material tool, not the area.
Pair with the Construction Calculator to turn area into concrete yards or aggregate tons, the Flooring Calculator for boxes and underlayment with waste, or the Paint Coverage Calculator for gallons per coat.