Area of a Circle Calculator

Calculate the area of a circle using radius or diameter. Get instant results with step-by-step solutions and visual formulas.

Input Method

Choose input type:

Radius (r)Diameter (d)

Enter radius:

Formula

A = π × r²

Where:

A =Area of the circle
π =Pi (≈ 3.14159)
r =Radius of the circle

Circle Diagram

Red line: Radius (r)

Green line: Diameter (d = 2r)

Shaded area: Circle area (A = πr²)

Common Circle Areas

RadiusArea

1 unitπ ≈ 3.14 units²

2 units4π ≈ 12.57 units²

3 units9π ≈ 28.27 units²

5 units25π ≈ 78.54 units²

10 units100π ≈ 314.16 units²

Understanding Circle Area

What is Circle Area?

The area of a circle is the amount of space enclosed within the circle's boundary. It's measured in square units and represents the total surface inside the circle.

Key Formulas

Area from radius: A = πr²
Area from diameter: A = π(d/2)² = πd²/4
Radius from area: r = √(A/π)
Diameter from area: d = 2√(A/π)

Real-World Applications

• Architecture: Calculating floor space for circular rooms
• Landscaping: Determining area for circular gardens or lawns
• Engineering: Computing cross-sectional areas of pipes
• Manufacturing: Material requirements for circular components
• Sports: Field dimensions for circular or curved areas

Tips for Accuracy

• Use more decimal places of π for precise calculations
• Double-check whether you have radius or diameter
• Ensure consistent units throughout your calculation
• Remember that area is always in square units

Frequently Asked Questions - Area of a Circle Calculator

The formula for the area of a circle is A = πr², where A is the area, π (pi) ≈ 3.14159, and r is the radius of the circle.

Tips

Enter the dimensions in the same unit for consistency.
Results update automatically as you type.
Use the unit selector to convert between different measurement systems.

Understanding Circle Area

What is Circle Area?

The area of a circle is the amount of space enclosed within the circle's boundary. It's measured in square units and represents the total surface inside the circle.

Key Formulas

Area from radius: A = πr²
Area from diameter: A = π(d/2)² = πd²/4
Radius from area: r = √(A/π)
Diameter from area: d = 2√(A/π)

Real-World Applications

• Architecture: Calculating floor space for circular rooms
• Landscaping: Determining area for circular gardens or lawns
• Engineering: Computing cross-sectional areas of pipes
• Manufacturing: Material requirements for circular components
• Sports: Field dimensions for circular or curved areas

Tips for Accuracy

• Use more decimal places of π for precise calculations
• Double-check whether you have radius or diameter
• Ensure consistent units throughout your calculation
• Remember that area is always in square units

Frequently Asked Questions - Area of a Circle Calculator

The formula for the area of a circle is A = πr², where A is the area, π (pi) ≈ 3.14159, and r is the radius of the circle.

Area of a Circle Calculator

Input Method

Formula

Where:

Circle Diagram

Common Circle Areas

Understanding Circle Area

What is Circle Area?

Key Formulas

Real-World Applications

Tips for Accuracy

Frequently Asked Questions - Area of a Circle Calculator

What is the formula for the area of a circle?

How do you calculate area from diameter?

What units can I use for circle area?

Why do we use π in the circle area formula?

What's the difference between radius and diameter?

Tips

Area of a Circle Calculator

Input Method

Formula

Where:

Circle Diagram

Common Circle Areas

Understanding Circle Area

What is Circle Area?

Key Formulas

Real-World Applications

Tips for Accuracy

Frequently Asked Questions - Area of a Circle Calculator

What is the formula for the area of a circle?

How do you calculate area from diameter?

What units can I use for circle area?

Why do we use π in the circle area formula?

What's the difference between radius and diameter?

Tips