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.

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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

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

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

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 gapsCenter 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 markingA 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.

Assumptions. Balanced load and line-to-line voltage assumptions behind this chart.

The chart uses planning outside diameters and the calculator-selected gap to document a parallel conduit bend layout.
Actual conduit dimensions, supports, rack hardware, and field spacing should be checked against product data and installation constraints.
Mixed-size conduit racks need separate documentation for each path because the center spacing and radius changes are not uniform.

Code and standard notes. Planning limits that should be checked before final equipment selection.

Use this as a field layout worksheet and verify conduit OD, support spacing, bend radius, enclosure entry, and clearance before final installation.

How to use this chart

1Set the conduit groupRecord conduit count, type, trade size, outside diameter, and desired face gap before comparing center-to-center spacing.

2Use the inner bend as referenceDocument the inner radius first, then list each outer radius, arc length, and mark offset returned by the calculator.

3Check rack width and entriesCompare total array width with support space, enclosure entry, rack spacing, and clearance before field bending.

Worksheet checklist. Record source basis, review gaps, and assumptions before using the chart result.

Record spacing inputsWrite conduit OD, face gap, center-to-center spacing, bend angle, and inner radius from the calculator result.
Record each conduit rowDocument radius, arc length, and mark offset for each conduit so the rack can be laid out consistently.
Record field verificationNote product OD, supports, spacing, enclosure entry, and clearance checks before treating the rack layout as final.

Common mistakes to avoid. Review these before turning chart current into an equipment decision.

Using face-to-face gap as center spacing and forgetting to add conduit outside diameter.
Applying the same bend mark to every conduit in a rack even though each outer conduit has a larger radius.
Forgetting to check total rack width at the support or enclosure entry before the concentric bends are made.

Frequently asked questions

These answers explain how to use the chart without turning a quick reference into a final design decision.

Why do outer conduits need longer arc lengths?

Outer conduits bend around a larger centerline radius, so their developed bend length is longer than the innermost run.

Can I use face gap as center spacing?

No. Center spacing is the conduit outside diameter plus the face-to-face gap. Using only the gap makes the rack too tight.

Can I mix conduit sizes in one concentric set?

Yes, but the calculator screen is organized around one selected size. Mixed-size racks need separate documentation for each conduit path.