Math Tools

Area Calculator

Select a shape and enter its dimensions to calculate the area. Get perimeter or circumference where applicable.

Shape

Base

Height

Length

Width

Area

50.00 square units

Perimeter30.00

FormulaA = l × w

ShapeRectangle

How it works

Select a shape from the dropdown menu. Enter the required dimensions (length, width, radius, etc.). The calculator instantly computes the area using the proper formula and displays it. Many shapes also show perimeter or circumference.

Varies by shape: Rectangle (A = l × w), Circle (A = π × r²), Triangle (A = (b × h) ÷ 2), and others.

Each shape has its own formula. Rectangles multiply length by width. Circles use pi times radius squared. Triangles use base times height divided by two. The calculator applies the correct formula for your chosen shape.

Input	Result	Notes
Rectangle: length 12, width 8	96 square units	A = 12 × 8 = 96; perimeter = 2(12 + 8) = 40
Circle: radius 5	78.54 square units	A = π × 5² = 3.14159... × 25 ≈ 78.54; circumference ≈ 31.42
Triangle: base 10, height 6	30 square units	A = (10 × 6) ÷ 2 = 30

Input

Result

Notes

Rectangle: length 12, width 8

96 square units

A = 12 × 8 = 96; perimeter = 2(12 + 8) = 40

Circle: radius 5

78.54 square units

A = π × 5² = 3.14159... × 25 ≈ 78.54; circumference ≈ 31.42

Triangle: base 10, height 6

30 square units

A = (10 × 6) ÷ 2 = 30

How to use the Area Calculator

Open the area calculator and select your shape from the dropdown

Enter the required dimensions (e.g. length and width for a rectangle, radius for a circle)

The calculator displays the area immediately

View the perimeter or circumference in the stats section where applicable

Copy the result or select a new shape to calculate again

Benefits

Instant results — no manual formula lookups or hand calculations

Supports seven common shapes — rectangle, square, triangle, circle, trapezoid, parallelogram, ellipse

Includes perimeter or circumference where applicable

Works with any unit (meters, feet, inches, cm) as long as dimensions are consistent

Eliminates formula memory burden — just select your shape and go

Tips & common mistakes

Common mistakes

Mixing units — if base is in meters, height must also be meters; do not mix feet and inches

Entering diameter instead of radius for circles — the calculator needs radius (half the diameter)

Forgetting the order of operations — triangle area needs base times height divided by two, not multiplied

Using the perimeter formula when you need area — they are completely different calculations

Tips

For circles, remember that radius is half the diameter; double-check before entering

Write down your dimensions before entering them to avoid re-entering the same values

The calculator supports decimals, so you can enter 7.5 or 10.25 if needed

Most real-world measurements in architecture use consistent units; pick one and stick with it

Frequently asked questions

What is the difference between area and perimeter?

Area measures the space inside a shape (square units). Perimeter measures the distance around the edge (linear units). A square with side 5 has area 25 and perimeter 20.

Can I use decimals for dimensions?

Yes. You can enter 5.5, 10.25, or any decimal value. The calculator handles fractional dimensions.

What units should I use?

Use any unit (meters, feet, inches, cm, km) as long as all dimensions are in the same unit. The result will be in square units of that measurement.

How do I find the radius of a circle?

Radius is half the diameter. If your circle's diameter is 10, the radius is 5. Measure from the center to the edge.

What is the formula for a trapezoid?

Area = ((Base A + Base B) × Height) ÷ 2. Add the two parallel bases, multiply by height, then divide by 2.

Is this calculator accurate?

Yes. The calculator uses precise mathematical formulas. Results are rounded to 2 decimal places for readability.