Area Calculator

Measure how much flat region a square, rectangle, triangle, circle, trapezoid, parallelogram or ellipse covers — flooring, turf, fabric or a printed sheet — and read the answer in the square of the length unit you chose.

How to use

Select the length unit every side already shares, or convert first so a centimetre is never multiplied by an inch.
Choose the outline that matches the region: a square needs one side, a rectangle two sides, a circle a radius, a trapezoid both parallel edges plus height.
Type only the lengths that shape asks for. Triangle, parallelogram and trapezoid height is the perpendicular drop, not a slanted edge.
Read the result in unit². That number is coverage, not how much a box holds and not how much wrap a solid needs.

How it works

Area answers “how much of the plane does this outline enclose?” Flooring a 5 m by 3 m room is 15 m² of plank. A circular flower bed of radius 2 m is 4π m² of soil surface. A trapezoid patio with parallel sides 6 m and 4 m and a 3 m perpendicular span is ½(6+4)×3 = 15 m². Those jobs fail if you treat the answer as litres or cubic metres.

The quiet mistake on triangles, parallelograms and trapezoids is feeding a slanted side as height. Height is the perpendicular distance between the bases. On a leaning parallelogram the slanted edge is longer than that drop; using it as height overstates the region. A rectangle is the special case where the side and the height coincide.

Circle mode on this page wants a radius. A pizza labelled by diameter, or a hoop you only measured around the rim, belongs on the circle calculator, which will turn diameter or circumference into r and then into area. Ellipse mode wants the two semi-axes — half the full widths — so a 10-by-6 oval is a = 5 and b = 3, not 10 and 6.

This tool is not a volume calculator. Filling a planter, a pool or a shipping carton is length cubed and lives on the volume page. It is also not surface area of a cube, box, cylinder or sphere: wrapping paper, paint on a tank or plating on a ball are still “squared,” but they are the skin of a solid, not a flat cut-out.

Sides must be positive. A zero-width rectangle is a line segment, not a region, and the form rejects it. Keep every length in one unit before you multiply; square inches and square centimetres are different quantities, and the page will not silently convert a mixed pair.

Formula

Square: A = s²
Rectangle: A = lw
Triangle: A = ½bh
Circle: A = πr²
Trapezoid: A = ½(a + b)h
Parallelogram: A = bh
Ellipse: A = πab

Worked examples

A 5 by 3 rectangle
rectangle 5 × 3 → 15 unit²
A circle of radius 2
r = 2 → 4π ≈ 12.566 unit²

Useful notes

Triangle here is base and height only. Three-side solving lives on the triangle page.
Circle from diameter or circumference is on the circle calculator.
Parallelogram and trapezoid height is perpendicular to the bases, never a leaning side.
An ellipse uses semi-axes a and b (half the full widths), then A = πab.
Zero or negative lengths are rejected; a real region has positive area.

FAQ

How do I find the area of a rectangle?: Multiply length by width. 5 × 3 = 15.
What unit is the answer in?: The square of your length unit. Inches in, square inches out.
Is this the same as surface area?: No. This is a flat region. Surface area wraps a 3-D solid — use that page for cubes, cylinders and spheres.
Is parallelogram height the same as its slanted side?: Only if the figure is a rectangle. Otherwise height is the perpendicular distance between the bases, which is shorter than the leaning side.
How do I find the area of a trapezoid?: Average the two parallel sides and multiply by the perpendicular height: A = ½(a + b)h. Both parallel sides and the height must use the same length unit.

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