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Area Calculator

Find the area of a rectangle, square, triangle, circle, trapezoid, parallelogram or ellipse, in square units, square feet, square meters and acres.

Results

ItemValue

Steps

StepWorking
Enter all sizes in the same unit. Height is measured at a right angle to the base. Answers are rounded to 4 decimal places.

Quick Answer

Area is the flat space inside a shape, in square units. A rectangle is length × width, so a 20 ft by 12 ft room is 240 sq ft. A circle is π × r², so a radius of 6 ft gives about 113.10 sq ft. A triangle is base × height ÷ 2.

Last updated: 2 November 2026 ·How we calculate this: standard area formulas

Table of Contents

How This Area Calculator Works

Pick a shape and a unit, then enter the sizes. The calculator shows the area in your unit and also in square feet, square meters and acres, with the formula and working.

Quick explanation: area = the space a flat shape covers, in square units such as ft².

  • Height: always measured at a right angle to the base.
  • Radius: half the diameter.
  • Rooms and floors: try our Square Footage Calculator.

How to Use the Area Calculator

  1. Choose the shape that matches your space.
  2. Choose the unit you measured in.
  3. Enter the sizes shown for that shape.
  4. Press Calculate.
  5. Read the area in your unit, square feet, square meters and acres, and follow the steps.

Core Formulas

  • Rectangle: A = l × w
  • Square: A = s²
  • Triangle: A = b × h ÷ 2
  • Circle: A = π × r²
  • Trapezoid: A = (a + b) ÷ 2 × h
  • Parallelogram: A = b × h
  • Ellipse: A = π × a × b

Key Terms

  • Area: the amount of flat space inside a shape.
  • Square unit: a square with sides of 1 unit, such as 1 sq ft.
  • Base and height: two sizes at right angles used for triangles and parallelograms.
  • Radius: the distance from the center of a circle to its edge.
  • Acre: a unit of land area equal to 43,560 sq ft.

Worked Example

A garden bed is a trapezoid. The parallel sides are 8 ft and 12 ft, and it is 5 ft deep.

  • A = (8 + 12) ÷ 2 × 5
  • A = 10 × 5 = 50 sq ft

Real-Life Examples

  • Flooring: a 12 ft by 14 ft room is 168 sq ft. With 10% extra for cuts, buy about 185 sq ft.
  • A round patio: a radius of 6 ft gives about 113.1 sq ft of pavers.
  • A gable wall: the triangle above a 24 ft wide wall, 8 ft high at the peak, is 24 × 8 ÷ 2 = 96 sq ft to paint.
  • A lot size: a 100 ft by 50 ft lot is 5,000 sq ft, or about 0.115 acres.

Area vs Perimeter

  • Area: the space inside a shape, in square units. Use it for flooring, paint, sod and land.
  • Perimeter: the distance around the edge, in plain units. Use it for fencing, edging and trim.
  • Same area, different perimeter: a 10 × 10 square and a 20 × 5 rectangle both have 100 sq units of area, but perimeters of 40 and 50.

Area Unit Conversions

UnitEquals
1 square foot144 sq in, about 0.0929 m²
1 square yard9 sq ft, about 0.836 m²
1 square meterabout 10.764 sq ft
1 acre43,560 sq ft, about 4,047 m²
1 hectare10,000 m², about 2.471 acres

Tips for Odd Shapes

  • L-shaped rooms: split them into rectangles and add the areas.
  • Cut-outs: subtract the area of any part you do not need.
  • Units: 1 sq yd = 9 sq ft, and 1 acre = 43,560 sq ft.

Common Mistakes to Avoid

  • Using diameter for a circle. The formula needs the radius, half the diameter.
  • Using a slanted side as the height. Height is measured at a right angle to the base.
  • Mixing units. Convert inches and feet to one unit first.
  • Converting square units like length. 1 sq yd is 9 sq ft, not 3.
  • Forgetting waste. Flooring and tile usually need 5% to 15% extra.

Frequently Asked Questions

Use the formula for the shape. For a rectangle, multiply length by width.

Multiply π by the radius squared. A circle with a radius of 3 has an area of about 28.27.

Multiply the base by the height, then divide by 2.

One acre is 43,560 square feet.

Area is the space inside a shape. Perimeter is the distance around it.

Split it into two rectangles, find each area, and add them together.

Multiply square feet by 0.0929. For example, 200 sq ft is about 18.58 m².

12 × 12 = 144 square feet.

Split it into simple shapes such as rectangles, triangles and circles. Find each area, then add them, or subtract any cut-outs.

Measure each room or section as rectangles, add their areas, and include hallways. Builders and appraisers may follow specific rules for what counts.

It is π × r² ÷ 2. For a radius of 4 ft, that is about 25.13 sq ft.

References & Sources

SourceUsed ForLink
Wikipedia, Area Area formulas for common shapes. https://en.wikipedia.org/wiki/Area
NIST, Unit conversion US customary and metric area units. https://www.nist.gov/pml/owm/metric-si/unit-conversion