Hoja de referencia de doblado
A conduit bending cheat sheet to print and tape in the lid of the box: the offset multipliers and shrink for 10° to 60°, the marks for the rises you bend every day in inches and millimetres, every bend in one line, and blanks for your own take-ups. Everything on this sheet is geometry, so it is true on any bender and any pipe. The blanks at the bottom are the figures that are not — your bender's take-ups — because those come off your shoe, not off a chart. Print it, fill the blanks in pencil, tape it in the lid of the box.
Multipliers and shrink
Between marks = rise × multiplier. Shrink = rise × shrink factor — add it to the overall LENGTH, not to mark 1. Both are plain ratios, so they work the same in inches or millimetres. Shop rules are the rounded figures for doing it in your head; the exact column is what the calculators use. The shop shrink column is computed here from the angle — the exact figure rounded up to the next sixteenth on purpose, so a mental layout errs long rather than short. That makes it heavier at every angle than the shrink figures most shop cards carry, so if you are comparing with someone else's card, that is why, and the difference is always in the safe direction. The shop multiplier column is not a rounding rule at all: those are the numbers the trade says out loud, and ×6 and ×3.9 are a shade heavy while ×2.6, ×1.4 and ×1.15 are a shade light. On a phone this table scrolls sideways — the last two columns are the saddle ones.
| Ángulo | Multiplier | Shop rule | Shrink factor (× rise) | Shop shrink (in per in) | As a saddle centre: outers | Outer multiplier |
|---|---|---|---|---|---|---|
| 10° | 5.759 | 6 | 0.087 | 1/8 | 5° | 11.474 |
| 15° | 3.864 | 3.9 | 0.132 | 3/16 | 7.5° | 7.661 |
| 22.5° | 2.613 | 2.6 | 0.199 | 1/4 | 11.25° | 5.126 |
| 30° | 2.000 | 2 | 0.268 | 5/16 | 15° | 3.864 |
| 45° | 1.414 | 1.4 | 0.414 | 7/16 | 22.5° | 2.613 |
| 60° | 1.155 | 1.15 | 0.577 | 5/8 | 30° | 2.000 |
Multiplier = 1 ÷ sin θ. Shrink factor = 1 ÷ sin θ − 1 ÷ tan θ (per inch of rise in inches, per mm of rise in mm). Saddle: centre-to-outer = depth × the outer angle's multiplier. Both saddles eat twice the offset shrink of their sloped angle; the three-point's centre-mark correction is one offset's worth of it. Any other angle: the multiplier calculator.
Marks for common rises
Between marks for an offset at each angle, and the shrink to add to the length. Marks are rounded to the nearest sixteenth or millimetre; shrink is rounded up, so the run errs long. Any rise not here: the offset calculator.
In inches (mm alongside)
| Altura | 22.5° marks | 30° marks | 45° marks | 30° shrink | 45° shrink |
|---|---|---|---|---|---|
| 1" / 25 mm | 2 5/8" / 66 mm | 2" / 51 mm | 1 7/16" / 36 mm | 5/16" / 7 mm | 7/16" / 11 mm |
| 2" / 51 mm | 5 1/4" / 133 mm | 4" / 102 mm | 2 13/16" / 72 mm | 9/16" / 14 mm | 7/8" / 22 mm |
| 3" / 76 mm | 7 13/16" / 199 mm | 6" / 152 mm | 4 1/4" / 108 mm | 13/16" / 21 mm | 1 1/4" / 32 mm |
| 4" / 102 mm | 10 7/16" / 265 mm | 8" / 203 mm | 5 11/16" / 144 mm | 1 1/8" / 28 mm | 1 11/16" / 43 mm |
| 5" / 127 mm | 13 1/16" / 332 mm | 10" / 254 mm | 7 1/16" / 180 mm | 1 3/8" / 35 mm | 2 1/8" / 53 mm |
| 6" / 152 mm | 15 11/16" / 398 mm | 12" / 305 mm | 8 1/2" / 216 mm | 1 5/8" / 41 mm | 2 1/2" / 64 mm |
| 8" / 203 mm | 20 7/8" / 531 mm | 16" / 406 mm | 11 5/16" / 287 mm | 2 3/16" / 55 mm | 3 3/8" / 85 mm |
| 10" / 254 mm | 26 1/8" / 664 mm | 20" / 508 mm | 14 1/8" / 359 mm | 2 11/16" / 69 mm | 4 3/16" / 106 mm |
| 12" / 305 mm | 31 3/8" / 796 mm | 24" / 610 mm | 17" / 431 mm | 3 1/4" / 82 mm | 5" / 127 mm |
In millimetres
For a metric job, round-millimetre rises. Nothing to convert and no fractions: read the figure straight off a millimetre tape.
| Altura | 22.5° marks | 30° marks | 45° marks | 30° shrink | 45° shrink |
|---|---|---|---|---|---|
| 25 mm / 1" | 65 mm | 50 mm | 35 mm | 7 mm | 11 mm |
| 50 mm / 1 15/16" | 131 mm | 100 mm | 71 mm | 14 mm | 21 mm |
| 75 mm / 2 15/16" | 196 mm | 150 mm | 106 mm | 21 mm | 32 mm |
| 100 mm / 3 15/16" | 261 mm | 200 mm | 141 mm | 27 mm | 42 mm |
| 150 mm / 5 7/8" | 392 mm | 300 mm | 212 mm | 41 mm | 63 mm |
| 200 mm / 7 7/8" | 523 mm | 400 mm | 283 mm | 54 mm | 83 mm |
| 250 mm / 9 13/16" | 653 mm | 500 mm | 354 mm | 67 mm | 104 mm |
| 300 mm / 11 13/16" | 784 mm | 600 mm | 424 mm | 81 mm | 125 mm |
The bends, one line each
- Doblez a 90° (stub)
- Mark = height − take-up, from the end. Arrow on the mark, measured end on the hook side, pull to square. calc
- Offset
- Mark 1 = layout measurement. Mark 2 = mark 1 + rise × multiplier. Both on the arrow, same angle, pipe rolled a half turn between, one plane. Shrink goes on the overall length. calc
- Silla de tres puntos
- C = centre measurement + one offset's shrink (the crown sits that much back along the bent pipe), on the notch, centre angle. Marks 1 and 2 = depth × outer multiplier either side of C, on the arrow, half the angle, the other way. The saddle eats twice that shrink out of the length. calc
- Silla de cuatro puntos
- Mark 1 = layout measurement. 2 = 1 + depth × multiplier. 3 = 2 + obstruction width. 4 = 3 + depth × multiplier, all measured from 1. Shrink (two offsets' worth) goes on the overall length. All on the arrow. calc
- Back-to-back
- Mark 1 = height − take-up, on the arrow. Bend it, then mark 2 = the back-to-back distance measured from the back of that 90 (or pre-mark it at height + distance − gain), on the star, hook facing the first 90. calc
- Kick 90
- 90 mark = height − take-up, arrow. Kick mark = kick rise ÷ sin θ down the tail, arrow, same plane. Pull the corner to 90° − kick angle so the stub stands plumb. calc
- Offset rodado
- True offset = √(rise² + roll²); roll angle = atan(roll ÷ rise). Lay out as an offset of the true offset with the pipe turned by the roll angle for both bends. calc
- Offset de caja
- Two small bends at a shallow angle, on the arrow: marks = depth × that angle's multiplier. 22.5° (×2.613) is what the calculator opens on; 10° (×5.759, shop ×6) if your shoe carries a line that shallow. calc
- Doblez segmentado
- Angle per bend = total ÷ count; spacing = 2 × radius × tan(half the per-bend angle); lay every mark out from one end. calc
- Take-up (find yours)
- Mark a scrap at a round figure, bend a 90 on the arrow, stand it up: height to the back − mark = take-up. calc
Bender references
- Arrow — the start of a bend: stubs, every offset mark, saddle outers, kicks.
- Notch (rim) — the centre of a 45: the middle mark of a three-point saddle. Check it once on scrap.
- Star — the back of a 90: the second mark of a back-to-back.
- Degree lines — read from the side, level with the shoe; pull a touch past for springback, the same touch on both bends of an offset.
- Hook — toward the end you measured from.
My bender
Fill in from your own test bends — measure your bender says how. One line per shoe and pipe. Saved them on the site? Print them as a pocket card with the stub marks worked out.
| Bender / pipe | Take-up | Ganancia | Desfase de muesca | Recuperación elástica |
|---|---|---|---|---|
Before every pull
- Rise centre to centre.
- Shrink added to the overall length (never to mark 1).
- Multiplier and angle from the same line.
- Take-up is mine, for this shoe and pipe.
- Right reference: arrow, notch, or star.
- Measured end on the hook side.
- Line all the way round the pipe.
- Foot on, then pull; sight down it before the second bend.
What is not on this sheet is the Code: bends per run between pull points, minimum radius, support spacing, fill. Those are the book's and the inspector's. bentright.com/bending-cheat-sheet