Bolt Tensile & Shear Capacity Calculator

What this tool does

Returns the allowable tension and shear for a structural bolt by grade and diameter, and multiplies out to a bolt group. Covers ASTM A307, A325, A449 and A490, SAE J429 grades, the F3125 metric structural grades A325M and A490M, and ISO property classes.

Results are ASD allowables for a bearing-type, snug-tight joint with one shear plane, based on the nominal shank area.

Formula

Two methods, depending on the fastener class. The ASTM grades divide a nominal stress by Ω = 2.00 — off Table J3.2 for A307, A325, A490 and the metric A325M and A490M, and off the threaded-part rule for A449. SAE grades and ISO property classes take the ultimate strength and divide by a 2.5 factor of safety.

Assumptions

Capacities use Allowable Stress Design (ASD) for a bearing-type, snug-tight connection with a single shear plane. Capacities are based on the bolt's nominal shank area (Ab). The three fastener classes below do not share a basis: read the one that matches your fastener.

• ASTM structural: A307, F3125 Gr A325, F3125 Gr A490, AISC Table J3.2 nominal stresses divided by Ω = 2.00. Allowable = Fn·Ab / Ω. F_nt / F_nv in ksi, with threads INCLUDED in the shear plane (N):
  • A307, Fnt 45 / Fnv 27
  • A325, Fnt 90 / Fnv 54
  • A490, Fnt 113 / Fnv 68
• ASTM A449, Same Ω = 2.00, different source for Fn. A449 has no row in Table J3.2; AISC 360 Section A3.4 designs it as a threaded part, so Fnt = 0.75 Fu and Fnv = 0.450 Fu (threads included), and Fu steps with diameter. Bearing-type connections only; A449 is not permitted in slip-critical joints. Quenched and tempered, used for anchor rods and bolts over 1-1/2 in. where F3125 does not reach:
  • A449, d ≤ 1 in: Fu 120 ksi, Fnt 90 / Fnv 54
  • A449, 1-1/8 to 1-1/2 in: Fu 105 ksi, Fnt 78.8 / Fnv 47.3
  • A449, over 1-1/2 in: Fu 90 ksi, Fnt 67.5 / Fnv 40.5
• SAE J429, Ultimate-strength basis, not an AISC one: T_ult = Fu·Ab, V_ult = 0.60·Fu·Ab, allowable = ultimate / 2.5. SAE J429 Fu: Gr 1 = 60, Gr 2 = 74, Gr 5 = 120, Gr 8 = 150 ksi. These are machine fasteners; a structural connection belongs on one of the ASTM grades above.
• Metric structural: F3125 Gr A325M, F3125 Gr A490M, The metric bolts AISC actually recognises, so they take the same Table J3.2 route as their imperial counterparts: Fn·Ab / Ω with Ω = 2.00, threads INCLUDED in the shear plane (N). F3125 covers M12 through M36; a custom diameter outside that range is flagged in the tool. F_nt / F_nv in MPa:
  • A325M, Fu 830 MPa, Fnt 620 / Fnv 372
  • A490M, Fu 1040 MPa, Fnt 780 / Fnv 469
• ISO metric property classes, Classes 4.6, 8.8 and 10.9, plus a custom entry. Ultimate-strength method and 2.5 factor of safety, not an AISC one. The tool applies 240, 640 and 900 MPa for the three classes; these are the class NOMINAL YIELD strengths, used where an ultimate strength would normally go. ISO 898-1 minimum tensile strengths are 400 / 800 (830 above M16) / 1040 MPa, so the results run conservative by roughly 16–67% depending on class. That is deliberate and is kept. An ISO property class is not a structural connection basis in any case: for a connection check use the F3125 metric grades above.
• Single shear, group capacity = number of bolts × single-bolt capacity. Multiple shear planes are evaluated separately.
• Combined tension and shear, tension and shear are checked independently, each against its own allowable. A bolt carrying both at once requires a separate interaction check per AISC J3.7; the tool does not perform one.
• Limitations, snug-tight bearing joints only; slip-critical (pretensioned) joints are not modeled. Estimates only, not a substitute for full connection design.

How capacities are derived

Area comes from the nominal shank diameter, then the fastener's class picks the method: a nominal stress over Ω = 2.00 for the ASTM grades — Table J3.2 for A307, A325, A490, A325M and A490M, the A3.4 threaded-part factors on Fu for A449 — or ultimate strength over a 2.5 factor of safety with a 0.60 shear ratio for SAE and the ISO property classes. The equations are in the Formula block above.

Worked example

Bolt hole sizing

Standard structural hole sizes per Steel Construction Manual Table J3.3.

• Bolts < 1", Hole diameter = bolt diameter + 1/16 in.
• Bolts ≥ 1", Hole diameter = bolt diameter + 1/8 in.
• Examples, 1/2" → 9/16", 3/4" → 13/16", 1" → 1-1/8", 1-1/2" → 1-5/8".
• Oversized & Slotted, Permitted only where allowed by the Manual; require added detailing.

Bolt length selection

Bolt Length ≈ Grip + Washers + Nut + Stick-Through.

• Grip Length, Total thickness of all connected material (plates, angles, channels).
• Add Components, Add washer and nut thickness.
• Stick-Through, End of bolt flush with the nut, or 1 to 3 threads past it after tightening.

Layout recommendations

Spacing and edge distances per AISC 360 Chapter J (Manual 16th Ed.); fastener material per ASTM F3125 / A307 / A449 and SAE J429.

• Spacing, Minimum 2⅔ × bolt diameter (Section J3.3); 3 × diameter typical for detailing.
• Edge Distance, Depends on diameter, hole type, and edge condition. Commonly 1-1/4 in. to 2 in.; verify against Table J3.4.
• Other Checks, This tool checks bolt capacity only. Bearing, tearout, block shear, net section, and prying must also be verified.

Field notes

• Threads excluded from the shear plane (an X connection) buys about 25% more shear. This tool works from the threads-included values; only claim the increase if the detail genuinely holds the threads clear, and take it from the Manual.
• Bolt capacity is rarely what fails. Bearing, tearout, block shear and net section have to be checked too; this tool checks the bolt only.
• A490 must never be hot-dip galvanized. If the connection needs a coating, that decision is made before the grade is.
• Double shear doubles the shear capacity, not the tension. Count the shear planes, not the plies.