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To bend a conduit offset: measure the rise centre to centre, pick an angle, and multiply the rise by that angle's multiplier — that is the distance between your two marks. Bend mark 1 on the arrow, roll the pipe exactly half a turn, bend mark 2 on the arrow to the same angle, and add the shrink to the length of the stick so the far end still reaches. A 6" (152 mm) rise at 30° puts the marks 12" (305 mm) apart and shrinks the run by about 1 5/8" (41 mm). The offset calculator does the arithmetic for any rise and angle.
Measure the rise
The rise is centre of the pipe where it runs now to centre of where it has to end up. Bottom to bottom is the same figure and easier to reach. Edge to edge counts the pipe's own thickness, and the offset comes out one diameter too big. A box offset into a knockout is the same bend with a very small rise.
Pick the angle
Use the shallowest angle the space allows: it pulls wire more easily and adds fewer degrees to the run, which count toward the limit in your code book. The price is length between the marks.
| Angle | Multiplier (between marks ÷ rise) | Shop rule | Shrink × rise |
|---|---|---|---|
| 10° | 5,759 | ×6 | 0,0875 |
| 22,5° | 2,613 | ×2,6 | 0,199 |
| 30° | 2,000 | ×2 | 0,268 |
| 45° | 1,414 | ×1,4 | 0,414 |
| 60° | 1,155 | ×1,15 | 0,577 |
Both are ratios, so they work in inches or millimetres: 0.268 × the rise is about a quarter-inch per inch, or 0.27 mm per mm. They are trigonometry, not a maker's table, and do not change with the pipe. The multipliers page has every angle.
Lay out the marks
Mark 1 goes on the layout measurement, from the end to where the first bend should start. The pipe before it stays straight, so nothing is added to it.
Mark 2 goes the rise × multiplier further along. Tape the running total from the end, not from mark 1 — see measuring and marking.
The shrink goes on the stick. The sloped section is longer than the flat distance it covers, so the far end comes back by the shrink. Cut the stick that much longer than the flat run.
Bending the offset, step by step
- Measure. The rise, centre of the pipe where it runs now to centre of where it has to go. And the layout measurement: from the end of the pipe to where the first bend should start.
- Work the figures. Pick the angle. Between marks = rise × the multiplier for that angle. Shrink = rise × the shrink figure for that angle; add it to the length of the stick.
- Mark. Mark 1 at the layout measurement from the end. Mark 2 at mark 1 plus the between-marks distance, taped from the same end. Lines all the way round, and a pencil line along the top of the pipe between them.
- First bend. Hook toward the end you measured from, arrow on mark 1, and pull to the angle, a touch past for springback.
- Roll a half turn. Slide the pipe along until mark 2 is on the arrow, then roll it exactly 180° so the first bend points the opposite way and the pencil line is dead underneath. Sight down the pipe to be sure.
- Second bend. Arrow on mark 2 and pull the same angle as the first, with the same touch past.
- Check. Lay the offset on the floor. Both straight parts should sit flat with no rock, and the step between them should measure the rise.
Rolled a half turn, the first bend points down into the floor, so most hands make the second bend in the air — handle on the floor, shoe up. The hand bender guide shows how.
The half-turn roll, and why a partial one fails
The second bend has to be exactly opposite the first, so the pipe goes back in the shoe rolled exactly 180°. Roll it 170° and the second bend is ten degrees out of plane: the far leg comes out pointing off to the side. That is a dog leg, and it is the most common way an offset goes wrong.
Before the first bend, draw a pencil line along the top of the pipe. For the second, roll until it is dead underneath, then sight down the pipe: the first bend points straight down, not a hair either way. A small dog leg can often be twisted out — fixing dog legs and kinks has how.
Worked examples
A 6" (152 mm) offset at 30°
Between marks: 6 × 2 = 12" (305 mm). Shrink: 6 × 0.268 = 1.61, 1 5/8" (41 mm). With the offset starting 30" (762 mm) from the end, mark 1 is at 30" (762 mm) and mark 2 at 42" (1067 mm), and the stick is cut 1 5/8" (41 mm) longer than the flat run.
A 4" (102 mm) offset at 45°
Between marks: 4 × 1.414 = 5.66, 5 11/16" (144 mm) on the tape (the shop's ×1.4 gives 5.6, near enough). Shrink: 4 × 0.414 = 1.66, 1 11/16" (42 mm). Mark 1 at 18" (457 mm), mark 2 at 23 11/16" (601 mm).
A metric offset: 5 7/8" (150 mm) at 30°
Between marks: 150 × 2 = 11 13/16" (300 mm). Shrink: 150 × 0.268 = 40.2, call it 1 9/16" (40 mm). If the offset starts 19 11/16" (500 mm) from the end, write 500 and 800 on the pipe, and cut the stick 40 mm longer than the flat run.
Check it lies flat
On a flat floor both straight parts sit down with no rock — a rock is a dog leg — and the step between them tapes as the rise. If the far leg climbs or dives, the two bends are not the same angle, usually because one got more overpull. Put the short one back in the shoe and pull.
A rack of offsets is the parallel offset job; rising and moving sideways at once is a rolled offset.
What goes wrong
Dog leg
What you see: the pipe rocks on the floor, the far leg points off to one side.
Why: the roll between bends was not a true half turn.
Fix: pencil line along the top, sight down before the second pull.
Short at the far end
What you see: a good offset that stops short of the box.
Why: the shrink was not added to the stick.
Fix: shrink on the cut length — never on mark 1.
Two bends the same way
What you see: the pipe curls up and does not come back level.
Why: no roll between the bends.
Fix: roll a half turn before the second bend.
Rise wrong, bends clean
What you see: both bends even, the step too big or too small.
Why: multiplier and angle from different lines, or the rise taken edge to edge.
Fix: angle and multiplier from the same line of the table; rise centre to centre. More on common mistakes.
Questions
- How do you bend an offset in conduit?
- Measure the rise centre to centre and pick an angle. Multiply the rise by that angle’s multiplier for the distance between two marks. Bend the first mark on the arrow, roll the pipe exactly half a turn, bend the second mark on the arrow to the same angle, and add the shrink to the length of the stick.
- What is the multiplier for a 30 degree offset?
- 2. Sin 30° is exactly one half, so the distance between the marks is twice the rise: a 6" (152 mm) rise at 30° puts the marks 12" (305 mm) apart. The shrink at 30° is 0.268 × the rise.
- Why is my offset twisted?
- That is a dog leg: the pipe was not rolled exactly half a turn between the two bends, so the second bend is a few degrees out of the plane of the first. Draw a pencil line along the top of the pipe first and roll until it is dead underneath.
- Which angle should I use for an offset?
- The shallowest the space allows. A shallow angle pulls wire more easily and adds fewer degrees to the run, which counts toward the limit in your code book. 30° is the everyday choice; 45° when the offset must happen in a short length; 10° or 22.5° for small rises and box offsets.