Where do the marks go on your conduit?

What the marks do

A bender gives you a shape, not a measurement: the pipe goes in, you line the arrow up with a pencil mark, and you pull. So the work of conduit bending is deciding where the marks go. An offset is two equal bends that move the pipe sideways or up by a set height, for example to step over a box knockout. A 90° stub-up brings the pipe out of the floor or up a wall at a set height. A 3-bend saddle carries it over a pipe or another conduit and back to its line. This calculator turns the height, the angle and the bender's take-up into marks measured from the end of the pipe, in inches and fractions of an inch or in millimeters.

The formulas

Between the two bends of an offset the pipe is the long side of a right triangle whose short side is the offset height. Its length is the height divided by the sine of the bend angle, so the multiplier is 1 ÷ sin θ (the cosecant). The pipe is shorter along the run than the path it takes, and for each inch of height the loss is csc θ − cot θ, which simplifies to tan(θ/2): that is the shrink per inch. A 90° stub needs a mark at the height minus the take-up, and the saddle uses the shop rule of 2.5 times the obstruction height for the outer marks. The same tan(θ/2) is the setback “K-chart” of the FAA's Advisory Circular 43.13-1B for sheet metal (0.2679 at 30°, 0.4142 at 45°), which is a handy check on the table below.

Worked examples

Offset. To move a pipe 6 inches with two 30° bends, the marks go 2 × 6 = 12 inches apart. The pipe shrinks by 1.50 inches on the chart's 1/4 inch per inch (the sharp-corner geometry says 1.61 inches). A 4-inch offset at 45° puts the marks 5.66 inches apart (the chart's 1.4 would give 5.60 inches). Stub-up. A 14-inch stub with the 5-inch take-up of a 1/2-inch EMT bender is marked at 9 inches from the end of the pipe, with the arrow on the mark. Saddle. Over a 3-inch obstruction the outer marks are 7.5 inches either side of the center mark, and the pipe shortens by 0.563 inch.

Limits of these numbers

The multipliers are exact, because they only describe the distance between marks. The shrink is not: the geometry treats the bends as sharp corners, but real bends have a radius, which is why the exact value is 6 to 40 percent above the chart in the table and why shop charts round down. Take-up belongs to the bender, not to the pipe size: the Navy's NAVEDTRA 14027 states that with power benders the take-up and the distance between bends differ from the hand-bender numbers, so use the maker's table for a power or hydraulic bender. And the code limits the total: the NEC allows the equivalent of four quarter bends (360°) between pull points. A conduit that springs back, a shoe that is worn or a second bend made on a slightly different line will each move the result by more than the arithmetic does.

What is the multiplier for a 30-degree offset?

2.0. The multiplier is 1 divided by the sine of the bend angle, so it is exactly 2 for 30°, 1.414 for 45° and 2.613 for 22.5°. Multiply the height of the offset by it to get the distance between the two marks: a 6-inch offset needs marks 12 inches apart. Benders usually print rounded values (2.6 for 22.5°, 1.4 for 45°, 1.2 for 60°) because the error is smaller than the springback of the pipe.

What is shrink and do I add it to my measurement?

Shrink is the length the bent pipe loses along the run, because the pipe takes the long way through the offset. For a 6-inch offset at 30° the bender chart gives 1/4 inch per inch, or 1.50 inches in all; the sharp-corner geometry gives 1.61 inches. If the finished pipe has to reach a fixed point past the offset, cut it that much longer, or add the shrink to the first mark. If the end of the pipe is free to float, ignore it.

What is take-up and where do I find mine?

Take-up (also called deduct) is the length of straight pipe a 90-degree bend uses up. For a stub-up you subtract it from the height you want, mark the pipe there and put the bender's arrow on the mark. Common hand benders for EMT list 5 inches for 1/2 inch, 6 inches for 3/4 inch and 8 inches for 1 inch; the number is stamped or cast on the bender, and the manufacturer's sheet is the authority. The Navy training manual NAVEDTRA 14027 warns that with power benders the take-up and the distance between bends differ from the hand-bender figures, and says to check the manufacturer's tables.

How many degrees of bend are allowed between pull points?

The National Electrical Code limits a run to the equivalent of four quarter bends, 360 degrees in total, between pull points such as boxes, conduit bodies and fittings. An older Navy manual quotes the same limit as four 90-degree bends under NEC article 370-18; in current editions the rule sits in each raceway article, for example 358.26 for EMT. An offset uses twice its angle (two 30-degree bends are 60 degrees) and a 3-bend saddle uses 90 degrees. The calculator shows the bend total it uses; add the other bends of the run yourself.

How does a 3-bend saddle work?

A saddle carries the conduit over an obstruction such as a pipe or another conduit and back down. The center bend is 45° and the two outer bends are 22.5° each, turned the opposite way. The outer marks sit 2.5 times the obstruction height from the center mark, and the shrink is about 3/16 inch per inch of height. Over a 3-inch obstruction that is 7.5 inches each way and 0.563 inch of shrink. The exact trigonometric spacing would be 7.84 inches; the 2.5 rule is the shop shortcut and is within about 4 percent of it.

Does this work for rigid, IMC and PVC conduit?

The multipliers and the saddle geometry do not depend on the pipe, so the offset marks are the same for EMT, IMC and rigid steel. The take-up does: a bigger trade size or a different shoe changes it, so type your own number into the take-up field. PVC is bent with heat in a heating box and then marked the same way; use a scrap piece to find how much it springs back.

Sources: right-triangle trigonometry (multiplier 1 ÷ sin θ, shrink tan(θ/2)); FAA Advisory Circular 43.13-1B (9/8/98), paragraph 4-56 and Table 4-7, for the same tan(θ/2) function; US Navy, NAVEDTRA 14027 (Construction Electrician), chapter 5, on power benders, and the Navy “Construction Electrician 3 & 2” manual, chapter 8, which cites the NEC limit of four 90° bends between pull boxes (NEC 370-18 in the edition it quotes); the current limit appears in each raceway article of NFPA 70, for example 358.26 for EMT (verify the number in your edition). The bender-chart rules and the take-up figures for 1/2, 3/4 and 1 inch EMT come from electrician training pages (Anvilfield, conduitbending.com, Intry) and are not set by a standard: your bender's instructions rule. Fill and wire: conduit fill calculator, box fill calculator and wire size calculator; angles and sides: right triangle calculator. How we check our calculators.