Area Calculator
Choose a shape, enter your dimensions, and click calculate.
Tip: Use the same unit for all dimensions.
What Is Area?
Area is the amount of surface inside a 2D shape. If perimeter tells you how far around a shape, area tells you how much space is inside it. You use area in everyday life for things like painting a wall, buying flooring, cutting fabric, landscaping a garden, or planning a room layout.
Area is always measured in square units, such as square meters (m²), square feet (ft²), or square centimeters (cm²).
Common Area Formulas You Should Know
- Rectangle: Area = length × width
- Square: Area = side × side
- Triangle: Area = (base × height) ÷ 2
- Circle: Area = π × radius²
- Trapezoid: Area = ((base1 + base2) ÷ 2) × height
How to Calculate Area Step by Step
1) Identify the shape
Before doing any math, make sure you know what shape you are working with. A wrong formula leads to a wrong answer, even if your arithmetic is perfect.
2) Gather measurements
Measure each required side or dimension. For triangles and trapezoids, the height means the perpendicular distance between bases, not the slanted side.
3) Keep units consistent
If one side is in centimeters and another is in meters, convert first. For example, 200 cm = 2 m.
4) Plug values into the formula
Substitute your numbers carefully. Double-check multiplications and division by 2 where needed.
5) Write the final unit as square units
If your dimensions were in feet, answer in ft². If in meters, answer in m².
Worked Examples
Rectangle Example
A room is 6 m long and 4 m wide.
Area = 6 × 4 = 24 m²
Triangle Example
A triangle has base 12 cm and height 9 cm.
Area = (12 × 9) ÷ 2 = 108 ÷ 2 = 54 cm²
Circle Example
A circle has radius 5 in.
Area = π × 5² = π × 25 ≈ 78.54 in²
Calculating Area of Composite Shapes
Many real-world spaces are not perfect rectangles or circles. For irregular plans:
- Break the shape into simple shapes (rectangle, triangle, etc.).
- Find each area separately.
- Add them together.
If the shape has cut-outs (like a rectangle with a circular hole), subtract the missing part from the full area.
Unit Conversion Tips
- 1 m = 100 cm, but 1 m² = 10,000 cm²
- 1 ft = 12 in, but 1 ft² = 144 in²
- Square units grow faster than linear units because both dimensions are converted.
Common Mistakes to Avoid
- Using perimeter formulas by accident
- Forgetting to divide by 2 for triangle area
- Using diameter instead of radius in circle formulas
- Mixing units without converting first
- Writing answers in plain units instead of square units
Quick Practice Questions
- Rectangle: length 9, width 7 → area = ?
- Square: side 11 → area = ?
- Triangle: base 14, height 5 → area = ?
- Circle: radius 3 → area = ?
Try solving these manually, then use the calculator above to check your answers.
Final Thoughts
Learning how to calculate area is one of the most useful math skills you can build. Start with core formulas, practice with simple shapes, then move to composite figures. With repetition, area calculations become fast, accurate, and practical for school, work, and daily life.