geometry and measurement
find the distance around a circle from a radius or diameter, then show it in the length unit you need.
circumference is the length of one complete trip around a circle. from radius r, use c = 2πr. from diameter d, use c = πd because d = 2r. the result is a length, never a square unit. π is approximately 3.14159265; the calculator uses the browser’s full math.pi value and rounds only the displayed answer.
for a circle with radius 5 m, c = 2 × π × 5 m = 31.4159 m, approximately. the same circle has a 10 m diameter. if you select centimeters as the output, 31.4159 m becomes approximately 3141.59 cm. a change of units changes the number, not the physical distance.
measure the radius from the center to the rim, or measure the diameter straight across through the center. a chord that misses the center is shorter than the diameter and will underestimate circumference. for a wheel, a tire’s printed nominal size may not match its loaded, rolling circumference; measure a full revolution if travel distance matters.
metric and us customary lengths are converted through meters: 1 in = 0.0254 m and 1 ft = 0.3048 m exactly. the tool assumes an ideal circle. material thickness, deformation, a noncircular outline, or measurement uncertainty can matter more than the final decimal places shown.
| Gegenstand | meaning | check |
|---|---|---|
| radius / diameter | the known straight-line circle dimension | a mode switch doubles or halves the visible number to preserve the circle. |
| input length unit | unit used by the entered dimension | changing units converts the entered value. |
| result length unit | unit of the distance around the circle | independent of the input unit. |
| Ergebnis | the calculated circumference | positive finite input is required. |
estimate the border needed for a circular bed from a measured diameter.
estimate edge length before adding joints and cutting allowance.
compare one geometric revolution with a measured travel distance.
a geometric circle is an approximation of a flexible or irregular physical object. add practical waste separately.
no. circumference is a one-dimensional length around the edge; area is the two-dimensional space inside the circle.
select diameter and use c = πd. the calculator also shows the corresponding radius.
the tool converts the entered length to preserve the same circle. for example, 1 ft becomes 12 in.
no. the tool requires a positive circle dimension and clears the result for zero, negative, blank, or nonfinite input.
last reviewed: october 23, 2026. calculations run in your browser. confirm dimensions and units for consequential work.
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