Circle Scale Calculator
Scale a circle’s radius and diameter by a non-negative factor. A factor of 2 doubles both lengths; a factor of 0.5 halves them.
How to use Circle Scale Calculator
1. Choose Measurement Unit, then enter Radius, Scale Factor without a unit suffix. 2. Use the selected ordinary, square or cubic unit for each measurement as explained below; changing the selector relabels inputs and does not convert them. 3. Select Calculate, or press Enter, and read scaled radius and diameter. 4. Select Select Copy result to copy the answer, or Reset to clear the form.
Why use this tool?
Resize a round drawing or circular feature while keeping its proportions and checking the new radius and diameter.
How the calculation works
New radius = original radius × scale factor. New diameter = 2 × new radius. Area changes by the square of the factor. Results use up to six decimal places. Tiny nonzero results below 0.000001 use scientific notation with six significant digits. Browser floating-point arithmetic can introduce small rounding differences. Inputs and calculated magnitudes must not exceed 9,007,199,254,740,991. Negative physical measurements and arithmetic underflow are rejected. Zero dimensions are treated as a degenerate limit where the formula allows them; divisors and sides of an actual triangle must be positive. Formula reference: https://openstax.org/books/prealgebra-2e/pages/c-geometric-formulas
Example
Radius = 5 cm and Scale Factor = 2 give Radius: 10 cm and Diameter: 20 cm.
Practical tip
Enter 1.5 for a 50% increase in length, rather than entering 50. A factor of zero collapses the dimensions to zero.
Frequently asked questions
Does doubling the radius double the area?
No. Doubling each length multiplies the area by four. This tool reports the new lengths, not the new area.
Can I use a negative scale factor?
This tool works with physical lengths and rejects negative factors. Use a non-negative factor; zero is allowed as a collapsed size.
Does changing Measurement Unit convert my numbers?
No. The selector states the unit of the numbers you enter and labels the answer. Convert measurements first when changing units. Area inputs use square units and volume inputs use cubic units; result precision follows the rounding method above.