Enter the obstacle height, bend angle, and (optionally) a shrink factor into the calculator to determine the bend spacing (“travel”) for a standard two-bend EMT offset. This calculator helps electricians lay out the correct spacing between bend marks and estimate the shrink allowance when bending around obstacles.
3/4 EMT Offset Formula
The following formulas are used for a standard two-bend offset (the geometry is the same for any EMT size; tool-specific take-up is separate from this travel calculation).
\begin{aligned}
OL &= \frac{OH}{\sin(BA)} \\
\text{Shrink allowance} &= S \cdot OH
\end{aligned}Variables:
- OL is the bend spacing / travel (distance between bend marks along the conduit centerline)
- OH is the offset height (rise)
- BA is the bend angle of each bend (degrees)
- S is the shrink factor (in/in), i.e., inches of shrink per inch of offset height (a common rule-of-thumb is S = 0.25 for a 30° offset)
To calculate travel (OL), divide the offset height (OH) by the sine of the bend angle (BA). If you need a shrink allowance to adjust your starting mark, multiply OH by the shrink factor S (often taken from a shrink table for common bend angles).
What is a 3/4 EMT Offset?
A 3/4 EMT offset is a bend in electrical metallic tubing (EMT) that allows the conduit to bypass an obstacle such as a wall or a beam. The offset is created by making two bends in the conduit at a specified angle. The layout typically uses the offset height (rise), the bend angle, and the travel (spacing) between bend marks; a shrink allowance may be used to adjust the first mark location.
How to Calculate 3/4 EMT Offset?
The following steps outline how to calculate the 3/4 EMT offset travel (bend spacing).
- First, determine the offset height (OH) in inches.
- Next, determine the bend angle (BA) in degrees (this is the angle for each of the two bends).
- (Optional) Determine a shrink factor (S) in in/in (often from a standard shrink table for common angles).
- Use the formula from above: OL = OH / sin(BA). (Optional shrink allowance: Shrink = S · OH.)
- Finally, calculate the travel (OL), which is the spacing between the two bend marks.
- After inserting the variables and calculating the result, check your answer with the calculator above.
Example Problem :
Use the following variables as an example problem to test your knowledge.
offset height (OH) = 6 inches
bend angle (BA) = 30 degrees
shrink factor (S) = 0.25 in/in (a common rule-of-thumb for a 30° offset). For these values: travel (OL) = 6 / sin(30°) = 12 inches, and shrink allowance = 0.25 · 6 = 1.5 inches.
