What makes an offset a rolled offset?

A plain offset moves the run in one direction — up, or across. A rolled offset moves it in two at once: it rises and shifts sideways between the same pair of fittings, so the jog is tilted out of the vertical plane. You still bend an ordinary offset; you just roll the pipe over first.

What is the true offset?

The true offset is the straight-line distance the run actually travels, the hypotenuse of the rise and the roll: √(rise² + roll²). That is the number you feed into the offset math, because the pipe does not know it is tilted — it only knows how far it has to jog.

What is the roll angle for?

The roll angle is how far to rotate the conduit — or your bends — off vertical before you bend the offset, so the jog leans the right way. It is atan(roll ÷ rise) measured from straight up. Roll the pipe to that angle in the bender, then bend the offset to the true offset.

Do I still add shrink on a rolled offset?

Yes, and against the true offset, not the rise. The run shrinks by the offset shrink of your bend angle applied to the true offset. Add it to your measurement the same as any offset or the far fitting lands short.

Rolled offset calculator

A rolled offset moves a run up and sideways at once. Enter how far it rises and how far it rolls across; the calculator gives the true offset (the real distance to bend for), the roll angle to rotate the pipe before you bend, and the distance between your two marks.

Worked example

Say the run has to rise 6 inches and move 4 inches sideways to meet the next box, bent at 30°. The true offset is √(6² + 4²) = 7.21 inches, and the roll angle is atan(4 ÷ 6) = 33.7°. Roll the pipe to 33.7° off vertical, then bend a 7.21 inch offset at 30°: the multiplier is 2, so the marks go 14 7/16 inches apart (7.21 × 2 = 14.42). Add the 30° shrink on the true offset — about 1 15/16 inches — to your measurement.

The formula

The rise and the roll are two legs of a right triangle; the true offset is the hypotenuse:

true offset = √(rise² + roll²) · roll angle = atan(roll ÷ rise)

Once you have the true offset, the rest is an ordinary offset: between marks = true offset ÷ sin θ and the same shrink as any offset, applied to the true offset. The roll angle only tells the pipe which way to lean so the jog points where you need it.

Exact vs. the field rule

The multiplier and shrink are the ordinary offset figures — they act on the true offset rather than on the rise. Rounded shop multipliers are fine for small jogs; on a long rolled offset the rounding drifts, and so does an eyeballed roll angle, so it is worth taking the true offset and the roll angle off the exact figures here.

Angle	Multiplier	Field rule	Shrink / in
10°	5.759	6	0.087 in
22.5°	2.613	2.6	0.199 in
30°	2.000	2	0.268 in
45°	1.414	1.4	0.414 in
60°	1.155	1.15	0.577 in

Questions

What makes an offset a rolled offset?: A plain offset moves the run in one direction — up, or across. A rolled offset moves it in two at once: it rises and shifts sideways between the same pair of fittings, so the jog is tilted out of the vertical plane. You still bend an ordinary offset; you just roll the pipe over first.
What is the true offset?: The true offset is the straight-line distance the run actually travels, the hypotenuse of the rise and the roll: √(rise² + roll²). That is the number you feed into the offset math, because the pipe does not know it is tilted — it only knows how far it has to jog.
What is the roll angle for?: The roll angle is how far to rotate the conduit — or your bends — off vertical before you bend the offset, so the jog leans the right way. It is atan(roll ÷ rise) measured from straight up. Roll the pipe to that angle in the bender, then bend the offset to the true offset.
Do I still add shrink on a rolled offset?: Yes, and against the true offset, not the rise. The run shrinks by the offset shrink of your bend angle applied to the true offset. Add it to your measurement the same as any offset or the far fitting lands short.

Related tools

Conduit offset calculator — the in-plane offset this builds on.
Three-point saddle calculator — over a round obstruction.
Conduit bending multipliers — exact multipliers and shrink.