Our comprehensive circle calculator offers four different calculation modes to find all circle properties from any known measurement:
🎯 From Radius Mode
Enter the radius to calculate area (A = πr²), circumference (C = 2πr), and diameter (d = 2r). Most common input when you know the distance from center to edge.
📏 From Diameter Mode
Input the diameter to find all other properties. Uses formulas: A = π(d/2)², C = πd, and r = d/2. Perfect when you can measure the full width of the circle.
🔄 From Circumference Mode
Enter the perimeter length to calculate radius (r = C/(2π)), area (A = C²/(4π)), and diameter (d = C/π). Useful when you can measure around the circle.
📐 From Area Mode
Input the area to find radius (r = √(A/π)), circumference (C = 2π√(A/π)), and diameter (d = 2√(A/π)). Great for space planning and surface calculations.
📊 Visual Features
• Interactive Circle Diagrams: See your circle with proper proportions
• Formula Display: All relevant formulas shown for educational value
• Real-time Results: Instant calculations as you input values
• Multiple Units: Works with any unit system (meters, inches, feet, etc.)
💡 Pro Tips
• All measurements should use the same units
• Results are precise to 4 decimal places
• Visual diagrams help understand relationships
• Switch between modes to verify calculations
• Perfect for geometry, engineering, and daily applications