Conduit Bending Calculator
Every apprentice learns the multipliers — two for a thirty degree offset, one point four for forty-five. Far fewer learn the second number that comes out of the same triangle. An offset pulls the conduit back along the run, and at thirty degrees it takes a quarter of an inch for every inch of offset. Six inches of offset is an inch and a half of conduit that is no longer where you measured it. This calculator gives the mark spacing and the shrink together, for offsets, three-bend saddles and stubs, because one without the other is how a stick gets scrapped.
- Distance between the two marks
- 12" 6" of offset ÷ sin 30° = 6" × 2.000. The field multiplier for 30° is 2, which is this number rounded.
- Shrink
- 1 5/8" An offset pulls the conduit back along the run by 6" × tan(30/2) = 0.268" per inch of offset — the trade figure is 1/4" per inch. Measure to where the end must land, then add this before marking, or the conduit finishes short of the box.
- The two marks
- 48" and 60" From the fixed end. The first mark is where the offset starts, the second is one bend spacing further along. Both bends are made at 30°, in opposite directions.
- Cut the stock longer by the shrink
- +1 5/8" The finished piece measures 1 5/8" shorter along the run than the same length of straight conduit, because the offset takes a diagonal path. Cut to the flat layout length and the end lands short of the box by exactly this much.
- Horizontal distance consumed
- 10 3/8" The straight-line distance the offset occupies along the run. Two offsets closer together than this cannot both be made.
- A shallower angle costs length, saves shrink
- 10° would need 36" A shallow offset is longer, shrinks less, and pulls far more easily — conductors dislike sharp changes of direction. A steep offset fits in a tight space and fights you on the pull. Where there is room, go shallow.
- Bends between pull points
- 360° maximum NEC 358.26 limits a run to the equivalent of four quarter bends — 360 degrees total — between pull points. Two offsets and a 90° already come to 150 degrees at 30°, and every degree of bend adds pulling tension exponentially rather than proportionally.
One triangle, two numbers
An offset is a right triangle laid into the conduit. The offset height is the opposite side, the distance between the two bends is the hypotenuse, and the angle is the bend angle. So the distance between marks is the offset divided by the sine of the angle, which is where the multipliers come from — two at thirty degrees, one point four at forty-five, two point six at twenty-two and a half.
The shrink is the same triangle read the other way. The hypotenuse is longer than the horizontal side it replaced, so the conduit ends up occupying less of the run than the length of pipe consumed. The difference works out to the offset multiplied by the tangent of half the angle.
Those figures reproduce the trade table exactly. A quarter of an inch per inch at thirty degrees, three eighths at forty-five, three sixteenths at twenty-two and a half. The table has been memorised for a century; the derivation is rarely written down next to it.
Knowing where the numbers come from matters when the angle is not one of the five on the bender. Any angle works — the sine and the half-angle tangent do not care.
Choosing the angle
A shallow offset is longer, shrinks less and pulls far more easily. A steep one fits into a tight space and makes the pull harder.
Pulling tension does not rise proportionally with bend angle — it compounds, because each bend multiplies the tension already in the conductor by a factor related to how far it wraps. Two shallow offsets are much kinder to a pull than one steep one, even though the total degrees are similar.
This is also why NEC 358.26 caps a run at 360 degrees between pull points, the equivalent of four quarter bends. It is easy to reach without noticing: two thirty degree offsets and a single 90 is already a hundred and fifty degrees, and a run with a couple of saddles in it can pass the limit before it looks complicated.
When a run is going to be near the limit, add a pull point rather than a bigger crew. Conductors damaged by an over-tensioned pull do not show it from the outside.
Take-up belongs to the bender, not the pipe
For a 90 degree stub, the number to subtract from the stub height is the take-up, and it is a property of the bending shoe rather than of the conduit. Common figures for EMT hand benders are five inches for half inch, six for three quarter, eight for one inch and eleven for inch and a quarter.
Those are common, not universal. Manufacturers differ, and the figure is stamped or cast into the bender for exactly this reason. Use the one on the tool in your hand.
The arrow on the bender marks the take-up point and faces the stub. The star or teardrop is for back-to-back bends, and the notch or rim mark centres a saddle. Using the wrong mark is the second most common bending error, after ignoring shrink.
One more figure appears when measuring between two 90 degree bends rather than from a cut end. A bend follows a radius, so the pipe travels a shorter path than the two legs suggest. That difference is the gain, and leaving it out makes a back-to-back run come out long.
What this is based on
- Offset geometry — distance between bends = height ÷ sin θ, shrink = height × tan(θ/2)
- NEC 358.26 — maximum 360 degrees of bend between pull points
- Common EMT hand bender take-up values (bender-specific; use the figure marked on the tool)
Bending geometry for EMT with a hand bender. Take-up figures vary between bender manufacturers and models — use the value marked on your tool. Rigid and IMC have different bending radii and gain, and mechanical or hydraulic benders differ again.
Frequently asked questions
What is conduit shrink?
The amount an offset shortens the conduit along the direction of the run. It equals the offset height multiplied by the tangent of half the bend angle — a quarter inch per inch at 30 degrees, three eighths at 45. Add it to your measurement before marking or the conduit finishes short.
What is the multiplier for a 30 degree offset?
Two. It is one divided by the sine of 30 degrees, which is exactly two. Forty-five degrees gives 1.414, rounded to 1.4 in the field, and 22.5 degrees gives 2.613, rounded to 2.6.
How do I mark a three-bend saddle?
Centre the middle mark on the obstruction, then measure out 2.5 times the obstruction height in each direction for the outer marks. The centre bend is 45 degrees and the two outer bends are 22.5 degrees in the opposite direction. Allow about 3/16 inch of shrink per inch of height.
What is take-up?
The distance from the end of the conduit to the back of a finished 90 degree bend. Subtract it from the stub height to find the mark. It belongs to the bender rather than the conduit, and the figure is stamped on the tool.
How many bends can a run have?
NEC 358.26 limits a run to 360 degrees total between pull points — four quarter bends. Offsets and saddles count toward it, and pulling tension rises exponentially with total bend angle rather than proportionally.