Bolt Spacing & Edge Distance — Complete Reference Tables

Bolt spacing and edge distance requirements for steel connections per AISC 360-22, AS 4100:2020, EN 1993-1-8, and CSA S16:2019. All values in inches and millimeters for direct use in connection design.

Minimum Bolt Spacing — AISC 360 Section J3.3

Minimum center-to-center spacing between bolts in any direction:

AISC 360-22 Section J3.3: The center-to-center spacing shall not be less than 2-2/3 times the nominal bolt diameter. A spacing of 3d is preferred for constructability.

Minimum Edge Distance — AISC 360 Table J3.4

Distance from center of standard hole to edge of connected part:

At Sheared Edges

At Rolled, Milled, or Gas-Cut Edges

Note: Sheared edges require larger minimum edge distances due to roughness of the cut surface. Rolled, milled, or thermally cut (gas-cut, plasma-cut, laser-cut) edges are smoother and allow smaller minimums.

Maximum Bolt Spacing — AISC 360 Section J3.5

Where t = thickness of thinnest outside plate or shape, Fy = specified minimum yield stress (ksi).

Maximum Edge Distance

Where t = thickness of the connected part.

Edge Distance for Oversized and Slotted Holes

Oversized and slotted holes require increased edge distances. Add the following increments to the standard hole edge distances above:

AS 4100:2020 — Minimum Edge Distance

AS 4100 Clause 9.4.2 uses hole diameter (d_h) rather than bolt diameter:

AS 4100 minimum edge distance = 1.5 x d_h (hole diameter), not 1.5 x bolt diameter. This gives slightly larger minimums than AISC for the same bolt size.

EN 1993-1-8 — Minimum Edge Distance

EN 1993-1-8 Table 3.3 provides minimum end distance (e_1) and edge distance (e_2):

Eurocode uses e_1 for end distance (along load direction) and e_2 for edge distance (perpendicular to load). Both are measured from bolt center to plate edge. Minimum spacing is 2.2d for spacing p1 (along load) and p2 (across load).

CSA S16:2019 — Minimum Edge Distance

CSA S16 Table 10 follows AISC values closely:

Practical Edge Distance Guide — Common Connections

For quick preliminary sizing, these edge distances work for most standard connections:

How Edge Distance Affects Bearing and Tear-Out Capacity

Edge distance directly controls two limit states in bolted connection design:

Bearing strength (AISC Section J3.10): For a single bolt near an edge, the bearing capacity is:

phiRn = phi x 1.2 x Lc x t x Fu

Where Lc = clear distance between hole edge and plate edge = edge distance minus half the hole diameter. Larger edge distance means larger Lc and higher bearing capacity.

Tear-out strength (AISC Section J3.10): When edge distance is small, the connection fails by tear-out (bolt tears a slot through the edge) rather than bolt shear or bearing. The tear-out capacity is:

phiRn = phi x 1.2 x Lc x t x Fu  (when deformation at service load is a consideration)
phiRn = phi x 1.5 x Lc x t x Fu  (when deformation at service load is NOT a consideration)

If edge distance is tight, tear-out may govern before bolt shear. Increasing edge distance by even 1/4 inch can significantly increase connection capacity.

AISC J3.3 Spacing Requirements — Detailed Breakdown

AISC 360-22 Section J3.3 specifies that the minimum center-to-center spacing of bolts in any direction shall not be less than 2-2/3 bolt diameters (2.67d). The preferred spacing for constructability is 3d. This minimum ensures adequate space for wrench clearance, prevents excessive stress concentration between adjacent bolt holes, and maintains sufficient net area between bolt rows for tension capacity.

Minimum Spacing by Bolt Diameter — Detailed Table

Wrench clearance typically governs over the 2.67d code minimum for bolts 3/4" and larger. A standard socket wrench for a 3/4" bolt requires approximately 1-3/4" between bolt centers, while the code minimum is only 2.0". Always verify that the selected spacing allows for wrench access, especially in confined connections like gusset plates and moment end plates.

Maximum Spacing for Weather-Tightness and Stitch Conditions

AISC 360-22 Section J3.5 limits maximum bolt spacing to prevent moisture ingress between connected parts and to ensure uniform load distribution:

For weathering steel connections, the tighter 14t limit ensures that the rust patina forms uniformly between faying surfaces. Wider spacing allows moisture to penetrate, creating uneven corrosion that degrades both appearance and structural performance. This is critical for exposed structures such as bridges, outdoor canopies, and architecturally exposed structural steel (AESS).

Maximum Edge Distance

AISC 360 Section J3.5 also limits maximum edge distance to the lesser of 12t and 6 inches, where t is the thickness of the connected part. This prevents the edge of the plate from curling away from the connected part under load. For thin material (t < 1/2"), the 12t limit governs: a 3/16" gusset plate has a maximum edge distance of only 2.25 inches.

Edge Distance Requirements per AISC J3.4 — Detailed Analysis

AISC 360-22 Table J3.4 provides minimum edge distances that vary by bolt diameter and edge type. The edge distance directly controls tear-out capacity, which is frequently the governing limit state for connections with limited edge distance.

Why Edge Distance Matters for Connection Capacity

The tear-out capacity per AISC Section J3.10 is:

phiRn = 0.75 x 1.2 x Lc x t x Fu

Where Lc = clear distance from hole edge to plate edge = edge distance minus half the hole diameter. For a 3/4" bolt with a 13/16" standard hole:

Increasing edge distance from the code minimum of 1-1/4" to 2" boosts tear-out capacity by 89%. In many practical connections, the edge distance is deliberately increased beyond the minimum to avoid having tear-out govern over bolt shear.

Edge Distance for Oversized and Slotted Holes

Oversized holes are used when fabrication tolerances require adjustment during erection. The edge distance increment accounts for the larger hole removing more material:

Long-slotted holes oriented transverse to the load direction require an even larger increment (+3/16"), while long-slotted holes parallel to the load are generally not permitted to transfer shear in bearing-type connections.

Staggered Bolt Spacing

When bolt holes are staggered (offset between adjacent rows), AISC 360 Section B4.3b provides the rule for evaluating net area along a staggered failure path. The critical net section may pass through staggered holes rather than a straight line:

An = Ag - sum(d_h x t) + sum(s^2 / (4 x g) x t)

Where s = stagger (longitudinal pitch between holes in adjacent rows) and g = gauge (transverse distance between rows). The term s^2/(4g) adds back area for each stagger, reflecting the longer failure path through staggered holes.

Staggered Spacing Design Example

A double-angle connection with two gauge lines at g = 3" and stagger s = 1.5" between rows. For 3/4" bolts (dh = 13/16") in 5/16" thick angles:

• Straight line net area through 2 holes: An = w x t - 2 x (13/16) x 5/16 = w x 0.3125 - 0.508 in^2
• Staggered path through 3 holes with 2 staggers: An = w x 0.3125 - 3 x 0.254 + 2 x (1.5^2 / (4 x 3)) x 0.3125 = w x 0.3125 - 0.762 + 0.117 = w x 0.3125 - 0.645 in^2

The staggered path removes more material (3 holes vs. 2) but the s^2/4g credit partially compensates. The designer must check all possible failure paths and use the one giving the lowest net area.

Standard Gauges for W-Shapes

The gauge is the transverse distance between bolt lines on a flange or web. Standard gauges for W-shapes are based on flange width and provide consistent, constructable connection layouts:

Standard gauges ensure that bolt patterns fit within the flange with adequate edge distance on both sides. For example, a W12x40 with bf = 8.01" and a 5-1/2" gauge provides edge distance of (8.01 - 5.50)/2 = 1.26" per side, meeting the minimum for 3/4" bolts at sheared edges (1-1/4").

Common Mistakes

1. Measuring from hole edge, not center: All code minimums are measured from bolt center to plate edge. Using hole edge gives dangerously small distances.

2. Confusing sheared and rolled edge requirements: Sheared edges need 1/4 to 3/8 inch more edge distance than rolled or gas-cut edges.

3. Ignoring hole type: Oversized holes (+1/8") and slotted holes (+3/16") require increased edge distances. Using standard hole minimums for oversized holes is non-compliant.

4. Insufficient wrench clearance: Code minimum spacing may not allow room for socket wrenches. For 3/4" bolts, 3" spacing provides adequate clearance. For 1" bolts, 3-1/2" is preferred.

5. Edge distance in both directions: Corner bolts have edge distance requirements in two perpendicular directions. Both must satisfy the minimum, and the smaller of the two often governs tear-out capacity.

Run This Calculation

• Bolted Connections Calculator — complete bolt group design with automatic spacing and edge distance checks
• End Plate Connection Calculator — moment connection bolt pattern design
• Fin Plate Connection Calculator — single plate shear connection design

See Also

• Bolt Hole Sizes — AISC Standard, Oversize & Slotted Dimensions
• AISC Bolt Capacity Table — A325 & A490, All Sizes
• Bolt Grades — A325, A490, 8.8, 10.9 Comparison
• Bolt Bearing & Tear-Out — Capacity and Edge Distance Effects
• Bolt Pattern Geometry — Pitch, Gage, and Layout

Disclaimer (educational use only)

This page is provided for general technical information and educational use only. It does not constitute professional engineering advice, a design service, or a substitute for an independent review by a qualified structural engineer. All real-world structural design depends on project-specific factors. You are responsible for verifying inputs, validating results with an independent method, checking constructability and code compliance, and obtaining professional sign-off where required.

Design Resources

Calculator tools

• Bolt Torque Calculator
• Bolted Connection Calculator
• Splice Connection Calculator
• Steel Bolted Connection Calculator

Design guides

• Bolt Torque Worked Example
• Bolted Connection Checklist
• Bolted Connection Worked Example
• AISC Shear Tab Example
• EN 1993-1-8 Bolted Connection Worked Example