Conduit Offset Multipliers and Shrink per Inch
Quick answer
The multiplier for a conduit offset is 1 ÷ sin(angle): multiply the offset height by it to get the distance between bends. Shrink = offset height × tan(angle/2). At 30° the multiplier is 2.00 and shrink is 0.268" per inch (about 1/4"); at 45° they are 1.41 and 0.414". A 6" offset at 30° has 12" between bends and 1 5/8" of shrink.
Every offset is a right triangle. The offset height is the side opposite the angle, the conduit between the two bends is the long side (the hypotenuse), and the run along the original line is the side next to the angle (the adjacent). Three ratios link them, and the multiplier chart in your pocket is just one of them written out.
The three ratios
- Sine (sin): opposite ÷ hypotenuse, or offset height ÷ distance between bends.
- Cosine (cos): adjacent ÷ hypotenuse, or run ÷ distance between bends.
- Tangent (tan): opposite ÷ adjacent, or offset height ÷ run.
Turn the sine upside down and you have the multiplier (the cosecant, 1 ÷ sin). Multiply the offset height by it to get the distance between the bends.
Multiplier and shrink per inch
between bends = height × multiplier = height ÷ sin(angle)shrink = height × tan(angle/2)- 10°: multiplier 5.76, shrink 0.087" per inch (about 1/16")
- 15°: multiplier 3.86, shrink 0.132" per inch (about 1/8")
- 22.5°: multiplier 2.61, shrink 0.199" per inch (about 3/16")
- 30°: multiplier 2.00, shrink 0.268" per inch (about 1/4")
- 45°: multiplier 1.41, shrink 0.414" per inch (about 7/16")
- 60°: multiplier 1.15, shrink 0.577" per inch (about 9/16")
Rolling offsets
When the conduit has to move up and over at once, the true offset is the diagonal, by Pythagoras: √(rise² + roll²). Bend that as an ordinary offset, then turn it so the bends lean out of plumb by atan(roll ÷ rise). A 6" rise with an 8" roll is a 10" offset, rolled 53.13° from plumb.
Worked example
- Offset height
- 6"
- Angle
- 30°
- Multiplier
- 2.00
- Between bends
- 12"
- Shrink (0.268" per inch)
- 1 5/8"
- Run it covers (adjacent)
- 10 3/8"
Why the calculator goes further
These formulas treat each bend as a sharp corner. A real shoe bends on a radius, which cuts the corner and uses a little less conduit. With a bender selected, the calculator allows for that from the shoe’s centerline radius, so the same offset on a 1/2" EMT hand bender comes out at 11 15/16" between bends and 1 1/2" of shrink. Pick Multiplier method in the bender list when you want the textbook numbers. The centerline radius page explains the difference.
Get the marks for your bender
BendMate works this out from your bender’s radius and deduct, flags a bend that won’t work, and shows you every mark.
Common questions
What are the conduit offset multipliers for each angle?
The multiplier is 1 ÷ sin(angle): 5.76 for 10°, 3.86 for 15°, 2.61 for 22.5°, 2.00 for 30°, 1.41 for 45° and 1.15 for 60°. Multiply the offset height by it to get the distance between bends.
How do you calculate shrink on a conduit offset?
Shrink = offset height × tan(angle/2), so tan(angle/2) is the shrink per inch of offset: 0.087" at 10°, 0.132" at 15°, 0.199" at 22.5°, 0.268" at 30°, 0.414" at 45° and 0.577" at 60°. A chart that says 3/8" per inch for 45° or 1/2" for 60° has rounded down.
Why doesn’t my bender match the multiplier chart?
The multiplier method treats each bend as a sharp corner, but a real shoe bends on a radius and uses a little less conduit. On a 1/2" EMT hand bender, a 6" offset at 30° comes out at 11 15/16" between bends and 1 1/2" of shrink, against 12" and 1 5/8" from the chart. BendMate allows for this from your bender’s centerline radius.