Area Calculator

What this calculator does

The Area Calculator measures the two-dimensional space inside four common shapes: rectangles, triangles, circles, and trapezoids. Area is expressed in square units, such as square feet, square meters, or square inches. Enter every length in the same unit, and the result is reported in that unit squared.

Area is useful in construction estimates, land planning, painting, flooring, and classroom geometry. A rectangle's area shows how much flooring covers a room. A triangle's area helps estimate a parcel of land or a roof section. A circle's area is needed for pipes, tanks, and round surfaces, while a trapezoid's area appears in road and drainage work.

How to use this calculator

1. Choose the shape: rectangle, triangle, circle, or trapezoid.
2. Enter the measurements shown for that shape.
3. Click Calculate.
4. Read the area and the related measurements in the result panel.

The default rectangle is 30 by 20, which gives an area of 600 square units. The triangle example uses sides 30, 45, and 50 and produces an area of about 666.5853. A circle with radius 30 has an area of about 2,827.4334, and a trapezoid with bases 30 and 45 and height 20 has an area of 750.

Area formulas

Rectangle: A = length × width
Triangle:  s = (a + b + c) / 2
           A = √(s(s − a)(s − b)(s − c))
Circle:    A = πr²
Trapezoid: A = ½ × (base 1 + base 2) × height

The triangle formula is Heron's formula, which works from three side lengths. The three sides must satisfy the triangle inequality: the sum of any two sides must be greater than the third side. The trapezoid formula assumes that the two bases are parallel and that the height is measured perpendicular to them.

What the results mean

The highlighted result is the area. The calculator also reports supporting values: the perimeter and diagonal for a rectangle, the perimeter and semiperimeter for a triangle, the circumference and diameter for a circle, and the median for a trapezoid. These values can help you check measurements or plan materials.

Results are rounded for display, while the underlying calculation keeps full JavaScript floating-point precision. Because π is irrational, circle results are always approximations.

Assumptions and limitations

• Every length must be entered in the same unit. The calculator does not convert between feet, meters, inches, and other units.
• All lengths must be greater than zero.
• Triangle sides must form a valid triangle. Degenerate triangles, where two sides add up to exactly the third side, are rejected.
• Only planar, two-dimensional shapes are supported. Surface area and volume are handled by separate calculators.
• The trapezoid tool only calculates area and median; it does not calculate perimeter because the leg lengths are not known.

Frequently asked questions

Do I need to use the same unit for every field?

Yes. The calculator treats all inputs as plain numbers and does not convert units. Convert every measurement to one unit first, then read the result in that unit squared. For example, if you enter feet, the area is in square feet.

Why do I need three sides for the triangle?

Three side lengths define a triangle completely, so Heron's formula can calculate its area without a height. If you know a base and height instead, the Triangle Calculator offers that alternative. Remember that not every group of three positive numbers forms a triangle.

How is a trapezoid different from a parallelogram?

A trapezoid has one pair of parallel sides, called bases, while a parallelogram has two pairs of parallel sides. The area formula used here averages the two bases and multiplies by the perpendicular height, which also works for a parallelogram when both bases are equal.

Reference tables

Area unit conversions

Example area comparisons

Source

Reference: Calculator.net — Area Calculator.

This page is for general educational and estimation purposes. Verify measurements and material quantities before making purchasing or construction decisions.