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Quickly calculate the area of a circle by entering the radius, diameter, or circumference. Supports custom units and precision settings.
Trigonometry Calculator
Calculate six trigonometric functions from radian values with custom decimal precision.
Inverse Trigonometric Function Calculator
Accurately calculate radian values for inverse trig functions like arcsin and arccos. Supports 6 function types and custom decimal precision.
Least Common Multiple (LCM) Calculator
Quickly calculate the least common multiple (LCM) of two or more integers. Supports space-separated number list input.
Prime and Composite Number Calculator
Instantly identify prime, composite, or special numbers. Supports batch checking and mathematical property analysis.
Trigonometry Calculator
Calculate six trigonometric functions from radian values with custom decimal precision.
Inverse Trigonometric Function Calculator
Accurately calculate radian values for inverse trig functions like arcsin and arccos. Supports 6 function types and custom decimal precision.
Least Common Multiple (LCM) Calculator
Quickly calculate the least common multiple (LCM) of two or more integers. Supports space-separated number list input.
Prime and Composite Number Calculator
Instantly identify prime, composite, or special numbers. Supports batch checking and mathematical property analysis.
Greatest Common Divisor (GCD) Calculator
An online tool to calculate the greatest common divisor (GCD) of multiple integers. Supports space-separated number lists.
Still calculating the area of a circle manually? Our Circle Area Calculator automatically outputs the area based on the radius (r), diameter (d), or circumference (C). The area of a circle is the amount of space it occupies in a 2D plane. The formulas used are A=πr² (for radius), A=π(d/2)² (for diameter), or A=C²/(4π) (for circumference). The result is presented in square units of length (e.g., square meters).
How do I calculate the area of a circle using its diameter?
Simply enter the diameter value. The tool automatically calculates it using the formula A=π×(d/2)². For example, a circle with a diameter of 10 cm has an area of approximately 78.54 cm².
How are the result units handled?
If the input unit is meters (m), the result is automatically displayed in square meters (m²). If no unit is provided, only the numerical value is output.
Input values must be positive numbers greater than zero. When calculating by circumference, ensure the value meets the geometric conditions for a circle. Non-numeric inputs will cause the calculation to fail. For sensitive data, we recommend not entering real-world dimensions.
Pi (π) is calculated using 15-digit precision (3.141592653589793). For engineering applications, we recommend keeping 4 decimal places. Typical examples: The area of a circle with a 5 cm radius is ≈ 78.54 cm², and a 10 m diameter yields ≈ 78.54 m². In educational settings, this tool can be paired with formula derivations to demonstrate unit conversion logic.
