Select whether you want to calculate using the Radius formula or the Diameter formula, enter the value, choose the unit and decimal places, and click Calculate Area.
Circle Area Calculator
Answer:
How to Use the Calculator
- Choose whether to use the Radius formula (S = π·r²) or the Diameter formula (S = π·d²÷4).
- Enter the radius or diameter value in the field. Use a period or comma as the decimal separator.
- Select the Unit of measurement (mm, cm, m, km, or in.).
- Choose the number of Decimal Places for the result.
- Click Calculate Area and the result will appear in the Answer field.
Circle Area Formula
The area of a circle is calculated using the formula:
S = π × r²
Where r is the radius and π ≈ 3.14159. If you only know the diameter d, remember that r = d ÷ 2, so the formula becomes:
S = π × d² ÷ 4
Practical Examples
| Radius (r) | Diameter (d) | Area (S) |
|---|---|---|
| 1 m | 2 m | ≈ 3.14 m² |
| 5 cm | 10 cm | ≈ 78.54 cm² |
| 7 m | 14 m | ≈ 153.94 m² |
| 10 mm | 20 mm | ≈ 314.16 mm² |
| 3.5 cm | 7 cm | ≈ 38.48 cm² |
Frequently Asked Questions
What is the formula for the area of a circle?
The area of a circle is given by S = π × r², where r is the radius and π ≈ 3.14159. If you know the diameter d, use S = π × d² ÷ 4, since r = d/2.
How do I calculate the area of a circle from the diameter?
Divide the diameter by 2 to get the radius and apply S = π × r². Alternatively, use S = π × d² ÷ 4. Example: d = 10 cm → S = π × 100 ÷ 4 ≈ 78.54 cm².
What value of π does the calculator use?
This calculator uses JavaScript's full π value (≈ 3.141592653589793), ensuring maximum precision before rounding to the chosen decimal places.
What is the difference between a circle and a circumference?
The circumference is the closed curved line that delimits the circle. The circle is the complete flat figure, including its interior. The formula S = π·r² calculates the area of the circle (inner region), not the circumference (the line).
How do I convert the result between units?
Area is always expressed in square units. If the radius was given in cm, the area will be in cm². To convert to m², divide by 10,000. To convert cm² to mm², multiply by 100.
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