Conduit offset bend calculator

How the offset and the stub are calculated

This page lays out a hand bend in two parts. An offset takes the height of the offset and the bend angle and gives the distance between the two bends, the shrink and the two marks to make on the conduit. A 90 degree stub takes the stub length and the conduit size and gives the mark to line up on the bender. The multipliers, the shrink figures and the bender deducts are the ones that Gardner Bender prints in its Hand Benders How To Guide, and the page shows the cosecant of each angle beside the rounded multiplier. Saddles, back-to-back bends and parallel bends are not covered.

Distance between bends

distance between bends = offset height x multiplier for the angleTable 2 of the guide gives 6.0 at 10 degrees, 2.6 at 22.5, 2.0 at 30, 1.4 at 45 and 1.2 at 60. A 6 inch offset at 45 degrees puts the bends 8.40 inches apart, and Table 3 of the guide reads 8-1/2 inches for the same offset.

Cosecant

exact distance between bends = offset height x 1 / sin(angle)The multipliers come from the cosecant of the angle, and the guide rounds them. At 10 degrees the cosecant is 5.759 against 6.0, and at 60 degrees 1.155 against 1.2. The default offset at 45 degrees gives 8.49 inches by the cosecant and 8.40 by the table.

Shrink

shrink = offset height x shrink per inch of offsetThe guide gives 1/16 inch per inch of offset at 10 degrees, 3/16 at 22.5, 1/4 at 30, 3/8 at 45 and 1/2 at 60. A 6 inch offset at 45 degrees shortens the conduit by 2.250 inches. The guide uses these figures only when working into objects, not away.

Marks on the conduit

mark Y = length to the offset + shrink, mark X = mark Y - distance between bendsWith 30 inches to the offset and the shrink added, mark Y is at 32.25 inches and mark X at 23.75 inches, taking the distance between bends to the quarter inch as the guide prints it. Make the first bend at X with the arrow on the bender, then reverse the bender and repeat at Y, as the guide directs. Working away from an object adds no shrink, so Y stays at 30 inches.

90 degree stub

mark from the end = stub length - bender deductTable 1 gives a deduct of 5 inches for 1/2 inch EMT, 6 for 3/4 inch, 8 for 1 inch and 12 for 1-1/4 inch. A 12 inch stub in 1/2 inch EMT is marked at 7 inches from the end.

Worked examples from the Gardner Bender guide

Table 2 of the guide lists the constant and the shrink per inch for each angle. The cosecant column is the exact 1 / sin(angle) for comparison. The guide rounds its constants. That is why 6.0 at 10 degrees sits against a cosecant of 5.759, and 1.2 at 60 degrees against 1.155, a gap you can ignore at the bench.

Table 3 of the guide recommends an angle for each offset depth from 1 to 10 inches and prints the distance between bends to the nearest 1/4 inch. The default case is its 6 inch row, 8-1/2 inches between bends and 2-1/4 inches of shrink. The tests of this page reproduce all ten rows from the formula.

Table 1 gives the bender deduct for a 90 degree bend. The guide prints no figure for 1-1/4 inch rigid or IMC. A 12 inch stub in 1/2 inch EMT is marked at 7 inches from the end of the conduit.

Eight cases below run through the same function the form uses. Five are rows of the guide's tables, one is the 60 degree bend that only Table 2 covers, one works away from an object so that no shrink is added, and one is the stub. With 30 inches to the offset, working away puts mark X at 21.50 inches where working into an object puts it at 23.75.

Standards and data sources

• Gardner Bender, Hand Benders How To Guide (GAR_BRO_032_1220) - Table 2 for the constant multipliers (6.0, 2.6, 2.0, 1.4 and 1.2) and the shrink per inch of offset for 10, 22.5, 30, 45 and 60 degrees. The recommended angle, the distance between bends and the shortening of offsets from 1 to 10 inches are in Table 3. Table 1 gives the bender deduct of a 90 degree bend in EMT, rigid and IMC, and the guide's offset layout steps define marks X and Y.
• ExpertCE, Geometry for Conduit Bending - The statement that the multipliers come from the cosecant of the bend angle, with 5.76 at 10 degrees and 1.15 at 60 degrees, and the note that a quarter inch of shrink per inch of offset at 30 degrees is an approximate industry value that varies with the angle and the technique.
• NFPA 70, National Electrical Code - The code that governs the raceway, its bend radius, the number of bends between pull points, its fill and its support. This page does not reproduce the text of the NEC, checks none of those rules, and leaves them to the installer and the authority having jurisdiction.

Limitations of this calculator

• The shrink chart is a guide. Gardner Bender calls it a guide for computing shrinkage and applies it only when working into objects, not away, and ExpertCE calls a quarter inch per inch at 30 degrees an approximate industry value that varies with the angle and the technique. A trial bend settles the figure.
• The marks assume that the bender behaves as the guide's does. Arrow, star, take-up and deduct differ between benders, so a bender of another make, a power bender or a bender with a different shoe has its own figures, and they take precedence.
• Only the five angles of Table 2 are offered, 10, 22.5, 30, 45 and 60 degrees. The page does not interpolate and takes no other angle, and the recommended angles of Table 3 appear as a warning without being forced.
• Saddles, back-to-back bends, parallel bends, kicks and segment bends are not calculated. The page cites no method for them and gives no figure.
• Distances are rounded to the tape. The distance between bends is read to the nearest 1/4 inch, as the guide prints it, and the marks and the shrink to the nearest 1/16 inch. Each result also shows the exact decimal.
• The page refuses an offset whose bends would sit closer together than the smallest hand bender in the guide can make, 2 x 3.69 inches x tan of half the angle, which is 4.26 inches at 60 degrees and 3.06 inches at 45 degrees. That limit is plain geometry applied to the smallest radius, and larger conduit needs more room. It also refuses a mark closer than 1 inch to the end of the conduit, a practical rule of this page and not a figure from the guide.
• The conduit rules of the NEC are outside the page. Bend radius, the number of bends between pull points and support come from the code and from the authority having jurisdiction. The conduit fill calculator covers fill.
• The 90 degree deduct comes from a table for one make of hand bender. Table 1 prints no figure for 1-1/4 inch rigid or IMC, so the page offers none, and larger sizes are not covered.
• Ranges are calculator limits and not code limits. The offset height runs from 0.25 to 36 inches, the length to the offset up to 240 inches and the stub from 1 to 120 inches.
• This is a planning estimate, not a shop drawing. Bend a scrap piece first. A licensed electrician, the manufacturer's data and the authority having jurisdiction decide the installation.

Common conduit bending mistakes

1. Taking the table multiplier as the exact geometry. The multipliers in the guide are rounded. At 10 degrees the table says 6.0 and the cosecant is 5.759, so a 6 inch offset reads 36 inches between the bends by the table and 34.55 inches by the cosecant, a gap of 1.45 inches. The same offset at 60 degrees reads 7.20 against 6.93.
2. Leaving the shrink out when working into an object. The conduit shortens as the offset forms. On the default 6 inch offset at 45 degrees the shrink is 2.250 inches, so a mark that ignores it lands 2.250 inches off and the run ends short of the object. Add the shrink to the length to the offset when working into an object.
3. Adding shrink when working away from an object. The guide applies its shrink figures only when working into objects, not away. With the default offset and 30 inches to the offset, working away puts mark Y at 30 inches and mark X at 21.50 (distance between bends taken to the quarter inch), where adding the shrink would move both 2.250 inches.
4. Choosing an angle that does not suit the offset height. Shallow angles spread the bends along the conduit. A 6 inch offset at 10 degrees needs 36 inches between the bends, where the 45 degrees that Table 3 recommends for it needs 8.40 inches. Pick the angle from Table 3 for the offset height and the room along the run.
5. Forgetting the deduct on a 90 degree stub. The mark is the stub length less the bender deduct. For 1/2 inch EMT the deduct is 5 inches, so a 12 inch stub is marked at 7 inches and not at 12, and a mark at 12 inches gives a stub 5 inches too long. A 1 inch EMT bend takes 8 inches off.
6. Not reversing the bender between the two bends. The guide has you make the first bend at mark X, reverse the bender and repeat at mark Y. Making both bends the same way bends the conduit further in the same direction, so it does not come back to parallel. Check the direction of each bend against the plan before you load the bender.

Common questions about conduit offset bends

Related calculators

• Conduit fill calculator The conduit size that holds the conductors, before the bends are laid out.
• Box fill calculator The box that the offset lines the conduit up with.
• Wire size calculator The conductors that the bent conduit will carry.
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