A walkthrough, end to end.
- 1
Pick a shape from the selector.
- 2
Enter the relevant dimensions; irrelevant fields disable.
- 3
The calculator returns the area along with the formula used.
Standard area formulas
Each shape has its own formula. The calculator picks the right one and applies it. Units are whatever you enter — keep them consistent across all inputs.
What you can do with this.
Painting a room
Wall area = length × height. For a 12 × 10 ft wall, 9 ft tall: each long wall = 108 sq ft, each short = 90. Total walls (4 walls, 396 sq ft) ÷ paint coverage (~350 sq ft/gal) = ~1.1 gallons. Get 1.5 to be safe.
Carpet / flooring
Rectangular room area + 5–10% waste. 12 × 14 ft room = 168 sq ft + 17 sq ft waste = 185 sq ft to order. Square footage drives most flooring purchases.
Roof shingles
Roof area + steepness factor. The flat (footprint) area times a pitch multiplier (1.05–1.4 typical) gives true surface area for shingles.
Lawn / landscaping
Grass seed and fertilizer applications are by square footage. Rectangular area is straightforward; irregular shapes break into rectangles + triangles + circles to total.
Concrete / patio
Volume = area × depth. Patio 10 × 12 ft × 4 inch deep = 120 sq ft × 0.333 ft = 40 cubic ft = 1.5 cubic yards. Concrete sold by the yard.
Wallpaper
Same square-footage logic as paint. Wallpaper rolls have specified area coverage on the package; divide total room wall area by coverage to get rolls needed.
Picture-frame area / matting
Frame inside dimensions × matt opening dimensions. Use the calculator to compute matt cut area when designing custom frames.
Area calculator 2026 — what's current
Smartphone AR apps measure rooms automatically (RoomScan, MagicPlan). For one-off calcs from known measurements, the calculator is fastest.
Frequently asked.
Whatever you enter. The math is unit-agnostic — keep all inputs in the same unit (all inches, all cm, all feet) and the output will match.
Decompose into standard shapes (rectangles + triangles + sectors). Compute each, sum. The calculator handles the standard pieces.
Area: 2D shapes. Surface area: total exterior of a 3D solid. The Surface Area Calculator handles 3D solids; this one handles 2D shapes.
No. Calculations run entirely in your browser.