Convert diameter to circumference and back. Enter whichever value the drawing gives you to get the other, plus the radius and the circle area.
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Request a Proposal →The relationship between diameter and circumference is defined by the constant pi. For machining applications, this is used daily to calculate turning diameters, O-ring groove dimensions, bolt circle circumferences, and part envelopes.
Pi appears in surface speed calculations (SFM = pi x D x RPM / 12), bolt circle coordinates, thread helix angles, circular interpolation (G02/G03), and countless other CNC formulas. Every machinist should know that pi is approximately 3.1416.
Circumference specifically refers to the distance around a circle. Perimeter is the general term for the distance around any closed shape. In machining contexts, the circumference of a turned part determines the cutting time for facing and contouring operations.
3.1416 (5 significant figures) is sufficient for 99% of machining work. Using 3.14 introduces ~0.05% error. For a 100 mm diameter, 3.14 gives a circumference of 314 mm vs the correct 314.16 mm -- a 0.16 mm error that might matter for precision fits.
Enter either the diameter or the circumference. The calculator instantly computes the other value plus the circle area. Use this to convert turning diameters to circumferences for surface speed calculations or to find the minimum stock diameter for a given part circumference.
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WORKING OUT A DIAMETER? Diameter callouts drive both tool size and incoming inspection. See how to specify and check a diameter.
We source carbide cutting tools from China for job shops. We do not own a factory, which is why we can quote your drawing against two or three plants that actually run your material.
Cutting formulas with the units worked through · Speed and feed starting points for all six ISO material groups · How to read a carbide grade past its ISO code. 12 pages.
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