EMT Offset Multiplier Chart

The multiplier for a 10 degree offset is 6.0, the constant bender-manufacturer charts print, and it is what this calculator applies. It is the rounded cosecant: 1 divided by sin(10 degrees) is 5.76. Shrink is 1/16 inch per inch of offset height. A 10 degree offset needs a lot of room: a 4-inch offset puts the marks 4 x 6.0 = 24 inches apart, so use it only where you have long straight runs and want the gentlest possible wire pull.

The multiplier for a 22.5 degree offset is 2.6 on the bender chart (exact 1/sin is 2.61), and the shrink is 3/16 inch per inch of offset height. For a 4-inch offset at 22.5 degrees, the marks are 4 x 2.6 = 10.4 inches apart and the run shrinks 4 x 3/16 = 3/4 inch. The 22.5 degree angle is popular because most bender heads have a dedicated 22.5 degree mark.

The multiplier for a 30 degree offset is 2.0, and it is the one angle where the bender chart and the exact 1/sin agree to the digit, because sin(30 degrees) = 0.5. Multiply the offset height by 2 to get the distance between your two bend marks, and use 1/4 inch of shrink per inch of offset height. This easy math is why 30 degrees is the standard angle taught in apprenticeship programs.

Multiplier = 1 / sin(bend angle), the cosecant, rounded the way the bender charts round it. For example, 1 / sin(45 degrees) = 1 / 0.7071 = 1.41, which the charts print as 1.4 and this calculator applies as 1.4; for an angle no chart lists, the calculator applies the unrounded 1 / sin. Shrink works differently. The per-angle shrink constants come from the published field chart rather than from a formula, and the 10 degree row sits about 29 percent below tan(angle / 2), so they are not a rounding of the geometry. The chart on this page covers every standard hand bender angle so you rarely need a formula on the job. For an angle it does not list, the calculator computes shrink as tan(angle / 2).

Shrink is how much shorter the conduit run becomes after you bend the offset. Multiply the offset height by the shrink-per-inch constant for your angle, then subtract that amount when measuring to your first mark from a fixed reference point. Example: your obstruction is 30 inches away and you are bending a 4-inch offset at 30 degrees. Shrink = 4 x 1/4 inch = 1 inch, so your first mark goes at 30 - 1 = 29 inches.

1/16 inch (about 0.063 inch) per inch of offset height for a 10 degree bend. Multiply the offset height by 1/16 to get the total shrink: a 4-inch offset at 10 degrees shrinks the run 4 x 1/16 = 1/4 inch. For comparison, shrink is 3/16 inch per inch at 22.5 degrees, 1/4 inch at 30 degrees, 3/8 inch at 45 degrees, and 1/2 inch at 60 degrees.

1/4 inch. When using 30 degree bends, the conduit shrinks 1/4 inch (0.25 inch) for every inch of offset height (answer c, from the choices 1/16, 1/8, 1/4, 1/2). So a 6-inch offset at 30 degrees shrinks the overall run 6 x 1/4 = 1-1/2 inches, which you subtract when locating the first bend mark.

No. The multiplier and shrink constants depend only on the bend angle, not the conduit size. A 30 degree offset uses a multiplier of 2.0 whether you are bending 1/2 inch or 1-1/4 inch EMT. Conduit size changes take-up, gain and deduct on 90 degree bends, and it changes whether an offset can be bent at all: at the size's NEC Chapter 9, Table 2 bend radius the two arcs need straight conduit between them, so a shallow offset at a steep angle is refused, and refused sooner in larger pipe. The marks themselves do not change. See the 90 degree deduction chart for the take-up values.

An offset counts as twice its bend angle, because it is two equal bends. A 30 degree offset adds 60 degrees; a 45 degree offset adds 90 degrees. NEC 358.26 limits EMT runs to 360 degrees of total bends between pull points, so a run with two 90s (180 degrees) and two 30 degree offsets (120 degrees) is at 300 degrees and has room for only one more small offset before it needs a pull box.