Conduit Bending Calculator

The offset. Two equal bends step the run sideways around something in the way. Between the marks the pipe follows the hypotenuse of a right triangle whose short side is the offset depth, so the distance between marks is the depth divided by the sine of the bend angle — the cosecant. That is all a multiplier is. csc(30°) is exactly 2; csc(10°) is 5.759, which the trade rounds to 6 because you can do that one in your head.

Shrink falls out of the same triangle. The sloped section is longer than the horizontal distance it covers, so the pipe consumes more length than the run advances and the far end arrives closer than it would have. It is a predictable consequence of the geometry rather than a tolerance, which is why it belongs in the cut length and not in a correction applied afterwards.

The 90° stub-up has one bend and nothing to measure between, so its arithmetic is a deduction instead. The curve consumes length; take-up is how much, subtracted from the height you want to find where the arrow goes. Note what that makes it — a fact about a tool rather than about geometry, and the one number on this page with no exact value to derive.

The three-point saddle crosses an obstruction rather than stepping around it. A centre bend lifts the run over and two outer bends bring it back down parallel to where it started. In the standard configuration the centre mark is bent to 45°, each outer mark to 22½°, and the outer marks sit two and a half times the obstruction height either side of centre.

A run of ½ in. EMT has to clear a 6 in. duct crossing its path. There is plenty of room either side, so a 30° offset it is — the friendliest angle to work with, because its multiplier is exactly 2.

Distance between the marks. Depth times the multiplier: 6 × 2 = 12 in. Mark the pipe where the offset should start, measure 12 in. further along, mark it again. Both marks get bent to 30°, arrows facing each other, both bends in the same plane.

Shrink. A 30° offset loses a quarter inch per inch of depth: 6 × ¼ = 1½ in. That is how much shorter the stick will be, end to end, once the bends are in it.

What that means at the saw. Suppose the finished run has to measure exactly 60 in. from the box to the coupling. Cut the pipe at 60 in. and bend it, and it will come out at 58½ — a stick in the scrap bin. Cut it at61½ in. and after bending it measures 60. The shrink figure is not a correction you apply afterwards; it is part of the cut length.

Now compare the angles. The same 6 in. offset at 45° would put the marks 6 × 1.4142 = 8½ in. apart and lose 6 × ⅜ = 2¼ in. to shrink. At 10° the marks go 36 in. apart and only ⅜ in. is lost. The trade-off is the whole art of choosing an angle: a shallow bend is an easy pull and a cheap shrink but needs a long clear run to develop in, while a steep one fits in tight quarters and costs you both length and pulling friction.

Six inches is also on the deep side for a single offset in ½ in. EMT. If the run were tight against a wall with only a foot of clear pipe either side, 45° or 60° would be the only options that fit — and the shrink allowance would need watching correspondingly harder.

The first table is the one worth photographing and keeping on your phone. It carries the published multiplier and shrink figures the calculator uses — and, next to each, the exact geometric value they come from. That second pair of columns is unusual for a trade table and it is there deliberately: it lets you see which figures arethe geometry, which have been rounded for convenience, and in which direction.

The second table is take-up by trade size, with the shortest stub each bender can produce and the mark for a 12 in. stub already worked out. Use it when you know the job and just need the number. Take-up is the figure most worth checking against your own tool before you rely on it, for the reason the notes below set out.