Whether you are working with Electrical Metallic Tubing (EMT), Intermediate Metal Conduit (IMC), or Rigid Metal Conduit (RMC), mastering the offset bend is essential for any electrician. An offset is used to route conduit around an obstacle or to change elevation to enter a knockout box.
How the Calculation Works
This calculator uses standard trigonometric multipliers used in the electrical trade to determine two critical values:
Distance Between Bends: This is the distance between your first and second mark on the conduit. It represents the hypotenuse of the triangle formed by the bend.
Shrinkage: Because the conduit travels a diagonal path, the total length of the run effectively shortens. You must add this shrinkage amount to your total measurement to ensure the conduit ends up where intended.
Standard Multipliers and Shrink Table
Professional electricians memorize the following multipliers (Cosecants) and shrink constants to make quick calculations in the field:
Bend Angle
Multiplier
Shrink per Inch of Depth
10°
6.0
1/16″ (0.063″)
22.5°
2.6
3/16″ (0.188″)
30°
2.0
1/4″ (0.250″)
45°
1.41
3/8″ (0.375″)
60°
1.15
1/2″ (0.500″)
Pro Tip: The 30° bend is the most popular choice because the multiplier is exactly 2.0. If you need to clear a 6-inch obstruction, your marks are simply 12 inches apart (6″ x 2).
How to Mark Your Conduit
Once you have your calculation:
Measure the distance to the obstacle.
Add the Shrink Amount to this distance and make your first mark (Mark 1). This accounts for the length lost during bending.
Measure back from Mark 1 by the Distance Between Bends calculated above and make Mark 2.
Place the conduit bender hook on Mark 1 for the first bend, and align Mark 2 with the arrow (or star/notch depending on orientation) for the second bend.
function calculateConduit() {
// Get input values
var depthInput = document.getElementById("offsetDepth");
var angleInput = document.getElementById("bendAngle");
var resultDiv = document.getElementById("result");
var depth = parseFloat(depthInput.value);
var angle = parseFloat(angleInput.value);
// Validation
if (isNaN(depth) || depth <= 0) {
resultDiv.style.display = "block";
resultDiv.innerHTML = "Please enter a valid obstruction height/depth greater than 0.";
return;
}
// Define Constants based on angle
var multiplier = 0;
var shrinkPerInch = 0;
// Using standard electrician approximations
if (angle === 10) {
multiplier = 6.0;
shrinkPerInch = 0.0625; // 1/16
} else if (angle === 22.5) {
multiplier = 2.613; // Often rounded to 2.6 in field, using precise for calc
shrinkPerInch = 0.1875; // 3/16
} else if (angle === 30) {
multiplier = 2.0;
shrinkPerInch = 0.25; // 1/4
} else if (angle === 45) {
multiplier = 1.414;
shrinkPerInch = 0.375; // 3/8
} else if (angle === 60) {
multiplier = 1.155;
shrinkPerInch = 0.5; // 1/2
}
// Calculations
var distanceBetweenBends = depth * multiplier;
var totalShrink = depth * shrinkPerInch;
// Convert decimals to fraction helper function
function toFractionString(decimal) {
var tolerance = 1.0 / 32.0;
var whole = Math.floor(decimal);
var fraction = decimal – whole;
if (fraction 0 ? whole + '"' : '0″';
// Iterate to find closest 1/16th or 1/32nd usually, let's do 1/16th for electrician standard
var denominator = 16;
var numerator = Math.round(fraction * denominator);
if (numerator === denominator) {
return (whole + 1) + '"';
}
if (numerator === 0) {
return whole + '"';
}
// Simplify fraction
while (numerator % 2 === 0 && denominator % 2 === 0) {
numerator /= 2;
denominator /= 2;
}
return whole > 0 ? whole + ' ' + numerator + '/' + denominator + '"' : numerator + '/' + denominator + '"';
}
// Generate Output
var outputHTML = "