Electrical reference chart
Concentric Bend Spacing Chart
Use this concentric bend spacing chart after the calculator result to document conduit OD, center-to-center spacing, inner radius, outer radii, arc lengths, and mark offsets.
Quick reference table
For a four-run 3/4 in EMT rack, 0.922 in OD + 0.500 in gap = 1.422 in centers. With a 12 in inner radius, the fourth run reaches a 16.266 in outer radius and a longer arc length. Use this chart to keep rack spacing, bend radius, and mark offsets aligned before bending a parallel set.
Sample EMT center spacing with 1/2 inch face gap
| EMT trade size | Planning OD | Face gap | Center spacing |
|---|---|---|---|
| 1/2 in | 0.706 in | 0.500 in | 1.206 in |
| 3/4 in | 0.922 in | 0.500 in | 1.422 in |
| 1 in | 1.163 in | 0.500 in | 1.663 in |
| 1-1/4 in | 1.510 in | 0.500 in | 2.010 in |
Four-run rack example using 3/4 inch EMT
| Run | Radius from 12 in inner radius | Arc length at 90 deg | Layout note |
|---|---|---|---|
| Inner run | 12.000 in | 18.850 in | Base reference |
| Run 2 | 13.422 in | 21.085 in | One center spacing outward |
| Run 3 | 14.844 in | 23.311 in | Two center spacings outward |
| Run 4 | 16.266 in | 25.551 in | Outer run needs longest developed length |
How to use this chart
Set the conduit group
Record conduit count, type, trade size, outside diameter, and desired face gap before comparing center-to-center spacing.
Use the inner bend as reference
Document the inner radius first, then list each outer radius, arc length, and mark offset returned by the calculator.
Check rack width and entries
Compare total array width with support space, enclosure entry, rack spacing, and clearance before field bending.
Formula basis
Center spacing = conduit OD + gap. Radius n = inner radius + (n - 1) x center spacing. Arc length = 2 x pi x radius x angle / 360.
- Conduit OD is the outside diameter for the selected conduit type and trade size.
- Gap is the desired face-to-face spacing between adjacent conduits.
- Inner radius is the centerline radius of the innermost conduit bend.
- Mark offset is the adjustment from the inner conduit reference for each outer conduit.
Worked examples
Four 3/4 inch EMT conduits with 1/2 inch gaps
Center spacing = 0.922 + 0.500 = 1.422 inches. Each outer conduit radius increases by another 1.422 inches from the inner reference.
Check rack width before marking
A four-run rack has three spaces between centers, so 3 x 1.422 = 4.266 inches between inner and outer centerlines, before adding half the outer conduit widths for total face-to-face width.
Related calculators
Concentric Bend Spacing Calculator
Calculate spacing and mark adjustments for parallel conduit runs on bends. Ensures consistent appearance with proper radius and developed length calculations for each conduit.
Segment Bend Calculator
Geometry screen for equal-angle segmented conduit bends. Returns bend angle, smooth-arc reference spacing, straight chord step, and optional bend-mark stations from a first-mark reference.
Parallel Roll Offset Calculator
Calculate rolling offsets for conduit that must move both horizontally and vertically. Provides true offset, roll angle, mark spacing, and shrinkage compensation.
Related charts
Segment Bend Layout Chart
Use a segment bend layout chart to document total angle, bend count, centerline radius, bend angle per mark, chord spacing, and field stations.
Parallel Roll Offset Chart
Use a parallel roll offset chart to document horizontal offset, vertical offset, true offset, roll angle, mark spacing, and rotation direction.
Frequently asked questions
These answers explain how to use the chart without turning a quick reference into a final design decision.