What Is Gain in Conduit Bending?
By Andrew ·
Quick answer
Gain is the conduit a bend saves by curving round the shoe instead of turning a sharp corner. For a 90 it is R × (2 − π/2), about 0.429 × the centerline radius, plus one OD when legs are measured to the back of the bend. Subtract it from the legs’ total for the cut length: about 2 1/2" for 1/2" EMT on a Greenlee hand bender.
Where gain comes from
A layout on paper, like the multiplier method, treats a bend as a sharp corner: the two legs run out to a point and meet. Real conduit wraps round the shoe and cuts that corner. The conduit in the bend is shorter than the two legs measured out to the corner, and the difference is the gain.
centerline gain of a 90 = 2 × R − R × π ÷ 2 = R × (2 − π/2) ≈ 0.429 × RStubs and legs are measured to the back of the bend, the outside of the conduit, which sits half an OD outside the centerline on each leg. So the gain you use at the bender adds one whole OD.
gain (back of 90) = R × (2 − π/2) + ODWhat gain is used for
cut length = stub + other leg − gain- Stub
- 12"
- Other leg
- 36"
- Gain
- 2 1/2"
- Cut length
- 45 1/2"
Each 90 in a stick takes off its own gain. A U made of back-to-back 90s has two corners, so it loses two gains.
cut length of back-to-back 90s = leg + distance between backs + leg − 2 × gainGain also moves marks. If you mark a second 90 on the straight conduit before bending the first, every 90 between the end and the mark pulls the mark one gain closer to the end.
- First stub
- 12"
- Distance between the backs
- 30"
- Gain
- 2 1/2"
- First mark, on the arrow
- 7" (12" − 5" take-up)
- Second mark, on the star
- 39 1/2" (12" + 30" − gain)
- Cut length with a 12" second leg
- 49"
The gain of real shoes
| Shoe | Centerline radius | Take-up (deduct) | Centerline gain | Gain (back of 90) |
|---|---|---|---|---|
| 1/2" EMT | 4 3/16" | 5" | 1 13/16" | 2 1/2" |
| 3/4" EMT | 5 1/8" | 6" | 2 3/16" | 3 1/8" |
| 1/2" rigid | 5 1/8" | 6" | 2 3/16" | 3 1/16" |
| 1/2" IMC | 5 1/8" | 6" | 2 3/16" | 3" |
| 1" EMT | 6 1/2" | 8" | 2 13/16" | 3 15/16" |
| 3/4" rigid | 6 1/2" | 8" | 2 13/16" | 3 13/16" |
| 3/4" IMC | 6 1/2" | 8" | 2 13/16" | 3 13/16" |
| 1-1/4" EMT | 9 5/8" | 11" | 4 1/8" | 5 5/8" |
| 1" rigid | 9 5/8" | 11" | 4 1/8" | 5 7/16" |
| 1" IMC | 9 5/8" | 11" | 4 1/8" | 5 7/16" |
Greenlee prints the radius and the take-up of each head. BendMate works the gain out from the radius and the conduit’s OD, which is why a rigid shoe in the same groove as an EMT one shows a slightly different gain.
| Bender | Shoe | Centerline radius | Gain (back of 90) |
|---|---|---|---|
| Klein Tools aluminum hand bender | 1/2" EMT | 4 5/8" | 2 11/16" |
| Greenlee 555 (Single shoe) | 2" EMT | 9 1/4" | 6 3/16" |
| Greenlee 881 (Hydraulic, Cam Track, one-shot 90° shoes) | 4" EMT | 20 7/8" | 13 7/16" |
The gain grows in step with the radius: double the radius and the centerline part doubles. On a big electric or hydraulic shoe it runs to several inches, so a cut length worked out with a hand bender’s gain, or with none, comes out long.
Gain at other angles
gain at any angle = 2 × R × tan(angle ÷ 2) − R × angle in radiansEach bend of an offset or saddle has a small gain too. The multiplier method ignores it, so on a real shoe the bends sit a little closer than the chart says and the shrink is a little smaller. It hardly shows on shallow bends in small conduit and matters more on steep bends and big shoes. BendMate works its marks out from your bender’s centerline radius and deduct, so the gain is already in them.
Get the marks for your bender
BendMate works this out from your bender’s radius and deduct, flags a bend that won’t work, and shows you every mark.
Free for offsets, saddles, 90s and kicks with a hand bender. No signup.
Common questions
What is gain on a conduit bender?
It is the conduit a bend saves by curving round the shoe instead of turning a sharp corner. You take it off the sum of the legs to find the cut length.
How do you calculate gain for a 90 degree bend?
Multiply the centerline radius by 2 − π/2, about 0.429. When the legs are measured to the back of the bend, as stubs are, add one OD of the conduit.
Is gain the same as take-up?
No. Take-up (deduct) tells you where to mark a 90 so the stub comes out right. Gain tells you how much shorter the conduit is than its two legs added together.
How do I find the gain of my own bender?
Bend a 90 in a piece of known length, measure both legs to the back of the bend, and subtract the length of the piece from their sum. What is left is the gain.