Calcs4All

APR 23 · 2026

Area calculator

Calculate area for rectangles, triangles, circles, trapezoids, and parallelograms.

What this calculator covers

Use this calculator to switch between common area formulas without changing tools every time the shape changes.

Each result keeps the selected formula visible so rectangle, triangle, circle, trapezoid, and parallelogram area work stays easy to verify.

Frequently asked questions

What units does the area result use?
The result is expressed in square units matching whatever unit you enter for the dimensions. If you measure in feet, the area is in square feet; if you measure in meters, the area is in square meters.
How do I find the area of a circle if I only know the diameter?
Divide the diameter by two to get the radius, then enter that radius value. The formula uses radius squared multiplied by pi.
What is the height of a triangle for area purposes?
Height is the perpendicular distance from the base to the opposite vertex — not the length of a slanted side. For a right triangle, height is simply the leg that meets the base at a right angle.
Why does the trapezoid formula use two base measurements?
A trapezoid has two parallel sides of different lengths. The formula averages those two bases before multiplying by height, which accounts for the way area tapers from the longer base to the shorter one.

Tool

Run the calculation

RESULT · AREA

â„–154

Primary result

40 sq units

For the selected rectangle with length 8, width 5, the area is 40 square units.

Length
8
Width
5
Formula
A = l x w
Area
40 sq units

Step-by-step solution

  1. 1.Read the rectangle measurements: length 8, width 5.
  2. 2.Apply the shape formula A = l x w, which becomes 8 x 5.
  3. 3.Evaluate the formula to get 40 square units.

Walkthrough

Visual walkthrough

Area always pairs a shape-specific formula with the measurements that feed it.

  1. 01

    Choose the matching shape rule

    A = l x w

    Each shape uses a different area relationship, so the calculator only validates the measurements tied to the selected figure.

  2. 02

    Substitute the measurements

    8 x 5

    The selected dimensions are inserted directly into the shape formula before solving.

  3. 03

    Read the covered area

    40 sq units

    The computed area is a two-dimensional measure, so the result is reported in square units.

    40 sq units