What the Area of Circle Calculator Does

You give the calculator one piece of information about your circle—either the radius (r), diameter (d), circumference (C), or even the area (A) itself. From that single input, it figures out all the other values. It also lets you choose units (mm, cm, m, in, ft, yd), pick how many decimals to show, and decide which π value to use (full Math.PI, 3.14, or 22/7). Internally, it keeps things consistent by converting lengths to meters (and areas to square meters), does the math, then converts back to the units you prefer.

Circle Formulas Explained

All circle calculations use these core formulas:

• Area:  A=πr²
• Circumference: C=2πr
• Diameter: d=2r

Given any one value, the calculator solves for the rest:

• From radius: Directly plugs into all formulas.
• From diameter: Divides by 2 to find r.
• From circumference: Rearranges to r=C/2π
• From area: Uses r=√A÷π

Once r is found, all other values follow simply.

Units, Conversion, and Precision

Input your value in your preferred units; the calculator converts to meters, does the math, and then displays results back in those original units. This prevents mix-ups and rounding errors. You control the number of decimal places for rough estimates or high-precision needs. You can also select how exact π should be; Math.PI is best for accuracy, while 3.14 or 22/7 are suitable for approximation. Changing π slightly affects all results.

What Results Show

Once you click Calculate, you get:

• Area (A) in your chosen area unit (e.g., m², ft²)
• Circumference (C), Radius (r), and Diameter (d) in your preferred length unit
• Area conversion table for quick comparison across units
• Optional breakdown explaining each calculation step for your numbers

Examples to Try

Example 1: Radius Given
A tabletop with r=0.6 m:

• Area: ≈1.13 m²
• Circumference: ≈3.77 m
• Diameter: 1.20 m

Example 2: Circumference Given
A running track with C=100 m:

• Radius: ≈15.92 m
• Diameter: ≈31.83 m
• Area: ≈795.77 m²

Example 3: Area Given
A garden with A=50 m²:

• Radius: ≈3.99 m
• Diameter: ≈7.98 m
• Circumference: ≈25.07 m

Common Pitfalls Avoided

• No need for manual unit conversion—the calculator handles it automatically.
• Results are rounded only at the end, keeping calculations accurate.
• You just enter the value you know; the tool selects the right formula and solves.