Conduit Bending Formulas, Explained

Conduit bending is field trigonometry, but you do not need to solve triangles on a roof at 6 a.m. Four formulas cover nearly every bend you will ever make: multiplier, offset spacing, shrink, and the gain of a 90°. Learn what each one means and when to trust it, and the bender starts doing exactly what you told it to.

The multiplier: 1 ÷ sin(angle)

The multiplier tells you how far apart to put your marks for an offset. It is the cosecant of the bend angle — 1 divided by the sine — and it is why spacing = offset height × multiplier works:

Electricians memorize the left two columns and stamp the table inside their hard hat. The third column — shrink — is where most layout mistakes come from.

Shrink: height × tan(angle ÷ 2)

An offset does not just move the conduit sideways; it also shortens the run. The geometric formula is shrink = offset height × tan(angle/2). At 30° that works out to exactly 1/4" of shrink per inch of offset — which is why the trade rule "subtract a quarter inch per inch of offset" exists. The table above rounds the other angles to the nearest shop-friendly fraction.

The 90° gain: 0.43 × radius

A 90° bend uses less conduit than the two straight legs it replaces. The gain is G = 2R × tan(45°) − R × π/2, which simplifies to about 0.43 × the bend's centerline radius. You need it when a run has a tight overall length budget; for most field work the bender's take-up marking absorbs it for you.

Worked example

You need a 3" offset at 30°. Mark spacing: 3" × 2.0 = 6" between marks. Shrink: 3" × 1/4" = 3/4" — subtract that from your measured run length before you mark. Two marks, two opposite 30° bends, and the conduit steps over 3" while losing 3/4" of length.

What formulas cannot tell you

Take-up is not a formula. It is a per-bender number stamped on the head (5" for 1/2" EMT, 6" for 3/4", 8" for 1") that describes where that particular bender starts its 90°. Always measure and verify on your own bender — the app's calibration tool exists for exactly this.