Area Calculator
Choose a shape, enter dimensions, and calculate area instantly.
What Is Area?
Area is the amount of surface a flat shape covers. If perimeter measures distance around a shape, area measures the space inside it. You use area all the time: figuring out paint needed for a wall, estimating the size of a room, planning garden beds, or comparing floor plans.
Area is always measured in square units, such as square centimeters (cm²), square meters (m²), square feet (ft²), or square inches (in²). The word “square” matters because area is two-dimensional: length × width.
Most Common Area Formulas
- Rectangle: Area = length × width
- Square: Area = side × side = side²
- Triangle: Area = (base × height) ÷ 2
- Circle: Area = π × radius²
- Parallelogram: Area = base × height
- Trapezoid: Area = ((base1 + base2) × height) ÷ 2
How to Calculate Area Step by Step
1) Identify the shape
The formula depends on the shape. If the figure is irregular, split it into simpler parts (rectangles, triangles, circles) and calculate each piece separately.
2) Measure all needed dimensions
Use a ruler, tape measure, or known dimensions from a drawing. For circles, measure radius (half the diameter). For triangles and parallelograms, make sure you use the perpendicular height, not a slanted side.
3) Keep units consistent
Don’t mix centimeters and meters in the same formula unless you convert first. For example, 120 cm and 3 m should be converted to the same base unit before multiplying.
4) Apply the correct formula
Substitute values carefully and calculate. Use parentheses in formulas like trapezoid area to avoid arithmetic mistakes.
5) Label the answer in square units
If your dimensions are in meters, your final area should be in m². If dimensions are in feet, final area is ft².
Worked Examples
Rectangle Example
A room is 5 m long and 4 m wide.
Area = 5 × 4 = 20 m²
Triangle Example
A triangle has base 10 cm and height 6 cm.
Area = (10 × 6) ÷ 2 = 30 cm²
Circle Example
A circle has radius 3 in.
Area = π × 3² = 9π ≈ 28.27 in²
Common Mistakes to Avoid
- Using perimeter formulas by accident: Perimeter and area are different measurements.
- Forgetting to square units: Write cm², m², ft², etc.
- Using slanted side as height: Height must be perpendicular to the base.
- Skipping unit conversion: Mixed units produce wrong results.
- Rounding too early: Keep extra decimals during calculation, then round at the end.
Area Conversion Quick Guide
Sometimes you need to convert final results for reports, construction estimates, or homework.
- 1 m² = 10,000 cm²
- 1 ft² = 144 in²
- 1 hectare = 10,000 m²
- 1 acre ≈ 4,046.86 m²
When Area Gets More Advanced
For irregular shapes, calculate area by decomposition: split the region into basic shapes, calculate each area, then add or subtract pieces. In coordinate geometry, area can be computed using formulas such as the shoelace method. In calculus, area under a curve is found by integration. But for most practical tasks, basic geometric formulas are enough.
Final Thoughts
If you can identify the shape, measure correctly, and apply the right formula, area problems become straightforward. Use the calculator above to check your work quickly and build confidence. With repeated practice, calculating area becomes a fast everyday skill useful in school, DIY projects, design, architecture, and finance-related planning.