Conduit Bending Pro

Professional electrician's calculator — metric (mm) · NEC reference  ·  ← electricalprotools.com

OD: -- mm ID: -- mm Min R: -- mm Wt: -- kg/m --
Offset Bend Calculator
offset mark distance th th
Please enter a valid offset distance.
Mark Distance
--
mm
Shrinkage
--
mm
1
Make your first mark at the start of the offset.
2
Measure -- mm along the conduit and make the second mark.
3
Bend both marks at --° in opposite directions.
4
Add -- mm to your total cut length to compensate for shrinkage (see below).

Distance = offset ÷ sin(--°)  ·  Shrinkage = distance × (1 − cos θ)

ⓘ What is shrinkage?

When you bend an offset, the angled section between your two marks travels diagonally. It uses up -- mm of conduit but only covers -- mm of actual run distance. That shortfall is shrinkage — pipe “spent” going up and back without advancing the run.

🔥 How experienced electricians handle it in the field
Bend the first offset, then measure. Don’t try to pre-calculate a single cut length. Instead:

1. Bend your first offset and place the conduit in position at box 1.
2. Measure from where the conduit ends to box 2.
3. Add the shrinkage for the second offset (-- mm) plus a couple of inches of spare.
4. Mark and bend the second offset.
5. Cut off the excess and connect.

This way you’re working off actual field measurements, not a pre-calculated number — much more forgiving, and any small variation in the first bend or box position is already accounted for.
⚠ If you do pre-cut to length
You must add shrinkage for every offset in the run before you cut — there is no adjustment after the fact. A conduit that comes up short after bending needs to be replaced with a longer piece.

Shrinkage per offset: 10° ≈ 9% of offset  ·  15° ≈ 13%  ·  22.5° ≈ 20%  ·  30° ≈ 27%  ·  45° ≈ 41%  ·  60° ≈ 58%

True Concentric Bend Calculator

All conduits start bending at the same reference line. The inner conduit makes the tightest sweep; each outer conduit sweeps a larger radius arc. Because the outer arcs are longer, each outer conduit needs that much more pipe in the sweep — calculated as the extra arc length (c-c × angle in radians per step).

#1 #2 #3 #4 c-c same c-c ✓ R₁ R₂ R₃ R₄ bend start
Field method: Install all conduits in the panel or box. Mark a reference line across all of them at the desired start-of-bend location. That line IS conduit #1’s bend mark. For each outer conduit, add the stagger amount (shown below) further from the box end. Remove conduit #1, bend it, reinstall. Remove conduit #2, mark the incremental bite spacings from its staggered mark, bend it, reinstall. Repeat. After bending, all conduits exit parallel at the original c-c spacing — no extra pipe needed, no cutting.
Suggested c-c for -- -- (OD + 50% gap): -- mm
Enter a valid inner radius, c-c spacing, and conduit count (2-8).
Incremental bite technique (outer conduits): Starting from the staggered mark, space additional marks at the bite spacing shown and make one bite at each mark, keeping the bender in the same plane every time. Work from the mark toward the free end of the conduit. The conduit gradually sweeps the full angle across all bites. Smaller bite angle = smoother sweep; 5° is standard for large rigid.
Industrial GRC Note (3"–6" Rigid): Concentric bends on large GRC are heavy industrial work — manufacturing plants, mine sites, petrochemical. A hydraulic bender rated for the pipe size is required. The inner conduit (#1) is bent with the hydraulic bender at its minimum radius. Outer conduits use the incremental bite technique because their larger bend radius cannot be made in a single bender shot without kinking the pipe. Mark the reference line across all conduits while they’re installed, then remove and bend one at a time. A 4" GRC section weighs approx. 27 kg (60 lb) per 3 m — always a multi-person operation.
3-Bend Saddle Calculator

Used to cross over an obstruction while keeping the conduit run parallel to the surface.

obstacle h M1 M2 M3 D (M1 to M2)
Please enter a valid obstruction height.
Mark 1 (outer bend -- --°)
Start of saddle.
--
Mark 2 (center -- --°)
D = -- mm from M1
-- mm
Mark 3 (outer bend -- --°)
D = -- mm from M2
-- mm
1
M1: bend --° UP (away from surface).
2
Measure -- mm to M2. Bend --° OPPOSITE direction.
3
Measure -- mm to M3. Bend --° UP again.
4
Conduit clears obstruction by -- mm and returns to original run line.

D = height ÷ sin(outer angle)  ·  center bend = 2 x outer angle

4-Bend Saddle (Box Offset)

Flat-topped rectangular saddle for wide obstructions. All four bends are the same angle.

obstacle width M1 M2 M3 M4
Enter valid obstruction height and width.
M1 to M2
--
mm
M2 to M3
--
mm
1
M1: bend -- UP.
2
Measure -- mm to M2: bend -- DOWN.
3
Measure -- mm (obstacle width) to M3: bend -- UP.
4
Measure -- mm to M4: bend -- DOWN.

Rise distance = height ÷ sin(θ)  ·  Top section = obstacle width

Conduit Specifications
TradeMetric OD (mm) ID (mm) Min R (mm) kg/m

Min bend radius per NEC Table 358.24 (EMT), 342.24 (IMC), 344.24 (RMC), 352.24 (PVC). Highlighted row = currently selected size. RMC/GRC available to 6" trade size. PVC Type A specs are approximate -- confirm with manufacturer data sheet.

NEC Permitted Uses -- Quick Reference
Type Outdoor / Exposed Direct Burial Concrete Physical Damage Art.
EMT Yes No No If listed 358
IMC Yes Yes Yes Yes 342
RMC/GRC Yes Yes Yes Yes 344
PVC Sch.40 SR mark req'd Yes Yes No -- use Sch.80 352
PVC Sch.80 SR mark req'd Yes Yes Yes 352
PVC Type A No No No No 352
ENT No -- no UV No No No 362

SR = Sunlight Resistant -- look for the "SR" stamp on the conduit. Both PVC Sch.40 and Sch.80 may carry the SR rating -- confirm before outdoor installation. ENT has no UV inhibitors and becomes brittle within 3-4 months outdoors. Outdoor ENT is a common code violation (NEC 362.12). Always verify with your local AHJ for amendments to the adopted NEC edition.

Direct Burial -- IMC & RMC/GRC: Steel conduit is NEC-permitted for direct burial, but bare steel corrodes over time in soil. When burying IMC or GRC, wrap the conduit with a protective pipeline tape (Denso tape, 3M Scotchrap, or equivalent pipeline wrap) before backfilling. Apply with a 50% overlap from coupling to coupling. Without wrapping, moisture and soil chemistry will attack the zinc coating and eventually the steel wall -- a failure that can be very expensive to repair once the trench is closed.

Offset Bend Multipliers

Mark distance = desired offset x multiplier

AngleMultiplierShrinkage/unit

Multiplier = 1 / sin(th)  ·  Shrinkage per unit = multiplier x (1 - cos th)

Concentric Bend Factors

Extra length per conduit = c-c spacing x factor

AngleFactor (rad)e.g. 150mm c-c
3-Bend Saddle Quick Ref

D = obstruction height / sin(outer angle)

CenterOutersMult x height
Formulas
Offset: mark_dist = offset / sin(th)
Shrinkage: offset x (1 - cos th) / sin th
Concentric (c-c): extra = c-c spacing x (th x pi / 180)
3-bend saddle: D = height / sin(th/2), center = 2 x (th/2)
4-bend saddle: rise = height / sin(th), top = obstacle width
C-C spacing: = conduit OD + wall clearance gap