Circumference Calculator

What this calculation does not cover

• Only a diameter is asked for, and the answer is that one figure multiplied by pi — nothing on the page distinguishes an outside diameter from a bore. Insulation, cladding, banding and protective wrap all run round the outside, so entering a pipe's inside diameter shortens the result by pi times twice the wall, roughly 38 mm (1.5 in) on a 6 mm (0.24 in) wall.
• Circumference rises in step with the diameter rather than with its square, so a tape reading five per cent over returns a wrap length five per cent over and nothing in the arithmetic averages that away. A tape laid across a post that misses the true centre reads short of the diameter, and that shortfall is carried through at full size.
• Pi is applied to whichever single width was typed, which only describes a true circle. A squashed duct or a buttressed trunk measured across its widest point comes out longer than the real path around it, and measured across its narrowest comes out shorter, with no second measurement asked for that could catch either.
• The value is the exact closing path around the circle, with no lap, seam allowance or tail included, and there is no overlap or waste field to add one. Strapping, spiral wrap, jacketing and cable ties are all cut longer than the girth they close on, and how much longer is left entirely to the person ordering.
• Each layer of a wrap sits on top of the one below it, so only the first turn runs round the diameter entered here. Lagging a pipe means working from the pipe outside diameter plus twice the insulation thickness, and one circle is drawn at the figure given with nothing added for the material's own build-up.
• The radius in the breakdown is half the diameter entered, put through the same conversion — a restatement of the measurement rather than a check on it. It confirms nothing about whether the object is truly round or whether the tape passed through its centre.