Bolt Shear & Tension Capacity Calculator (8.8 / 10.9 / A325)
Check a bolted connection to Eurocode 3 (EN 1993-1-8) or AISC 360 LRFD/ASD — tension and shear resistance of M6–M36 and 1/2–1-1/2 in bolts in grades 4.6 to 12.9, A307, A325 and A490, single or double shear, threads in or out of the shear plane, combined loading, plate bearing and tear-out, slip resistance, edge distances, preload and tightening torque, and how many bolts the load needs.
How it works
Eurocode 3: F_t,Rd = k2 f_ub A_s ÷ γ_M2 (k2 = 0.9, 0.63 countersunk) · F_v,Rd = α_v f_ub A ÷ γ_M2 per shear plane (α_v = 0.6 for 4.6/5.6/8.8 or any shank plane, 0.5 for 4.8/5.8/6.8/10.9 through threads) · F_v,Ed/F_v,Rd + F_t,Ed/(1.4 F_t,Rd) ≤ 1 · F_b,Rd = k1 α_b f_u d t ÷ γ_M2 · F_s,Rd = k_s n μ (F_p,C − 0.8 F_t,Ed) ÷ γ_M3. AISC 360: φR_n = 0.75 F_n A_b (LRFD) or R_n ÷ 2.00 (ASD) with F_nt = 0.75 F_u, F_nv = 0.450 F_u (N) or 0.563 F_u (X) · F′_nt = 1.3 F_nt − F_nt f_rv ÷ (φ F_nv) · bearing R_n = 1.2 l_c t F_u ≤ 2.4 d t F_u · slip φR_n = μ D_u h_f T_b n_s · preload F_p,C = 0.7 f_ub A_s · torque ≈ 0.2 F d
A bolt resists tension across its threaded core and shear across whatever cross-section the joint plane cuts, so both capacities scale with the ultimate strength of the grade — the first number of the marking times a hundred, in megapascals, or 60, 120 and 150 ksi for A307, A325 and A490 — and with the stress area or shank area. Eurocode 3 multiplies tension by 0.9 for the notch of the threads and shear by 0.6 (0.5 for the less ductile classes when the threads are in the plane), divides by the partial factor γ_M2 and limits combined loading with an interaction that lets a bolt carry full shear and still some tension. AISC 360 uses the nominal bolt area with reduced stresses instead — 0.450 F_u in shear when the threads are included — and a φ of 0.75 (LRFD) or Ω of 2.00 (ASD). The bolt is only half of the connection: the plate can crush or tear out in front of the bolt, so the calculator also checks bearing from the plate thickness, steel grade and edge distances, and it flags distances below the code minimums. In a slip-resistant joint the bolts are preloaded to 70% of their ultimate strength so friction carries the load; the slip check uses the friction class of the faying surfaces. The number of bolts needed is the smallest group that passes every check.
Worked example
An M16 grade 8.8 bolt with threads in a single shear plane has a design tension resistance of 0.9 × 800 × 157 ÷ 1.25 = 90.4 kN and shear resistance of 0.6 × 800 × 157 ÷ 1.25 = 60.3 kN. Four of them carrying 60 kN of tension and 80 kN of shear see 15 and 20 kN each — 17% and 33% — a combined utilisation of 20 ÷ 60.3 + 15 ÷ (1.4 × 90.4) = 45%. In a 10 mm S275 plate with e1 = 40, e2 = 30 and p1 = 60 mm (d0 = 18 mm), α_b = 40 ÷ 54 = 0.741 and k1 = 2.5, so bearing is 2.5 × 0.741 × 430 × 16 × 10 ÷ 1.25 = 102 kN per bolt — 20% used, so bolt shear governs; even 2 bolts would pass, at 90% combined. Full preload would be 88 kN at roughly 281 N·m. To AISC LRFD, a 1 in A325 bolt with threads included carries 0.75 × 54 × 0.785 = 31.8 kips in single shear and 53.0 kips in tension.
Sources: EN 1993-1-8:2005 Eurocode 3 — Design of joints (Tables 3.3 and 3.4) · AISC 360-22 Specification for Structural Steel Buildings, Chapter J · RCSC Specification for Structural Joints Using High-Strength Bolts
Frequently asked questions
What does 8.8 mean?
Ultimate tensile strength 8 × 100 = 800 MPa, and yield 0.8 × 800 = 640 MPa. 10.9 is 1,000 MPa ultimate, 900 yield. The stress area A_s (slightly larger than the root area) is what carries tension.
Why is the shear capacity lower with threads in the shear plane?
The threaded part has less steel than the shank — an M16 has 157 mm² of stress area against 201 mm² of shank — and for grades 4.8, 5.8, 6.8 and 10.9 Eurocode 3 also drops the shear factor from 0.6 to 0.5. AISC applies the same idea with 0.450 F_u for threads included against 0.563 F_u excluded. Specify a bolt with a long enough shank to keep the threads out of the plane where shear matters.
Eurocode 3 or AISC — which should I use?
Use the code your project is designed to: Eurocode 3 (EN 1993-1-8) in Europe and many other countries, AISC 360 in the United States. Eurocode loads and AISC LRFD loads are factored; AISC ASD uses service loads with a safety factor of 2.00 on the bolt. Results differ by a few percent for the same bolt.
What edge distances do bolts need?
EN 1993-1-8 asks for end and edge distances of at least 1.2 d0 and a pitch of at least 2.2 d0, where d0 is the hole diameter (bolt + 2 mm for M16–M24). AISC asks for spacing of at least 2-2/3 d (3 d preferred) and minimum edge distances from Table J3.4, about 1.25 d for standard holes. Larger distances raise the bearing resistance up to its cap.
Can I rely on the torque table for preload?
Only to about ±25%: friction in the threads and under the head varies with lubrication, plating and surface finish. Where preload matters (slip-critical or fatigue joints), use turn-of-nut, load-indicating washers or calibrated wrenches per the standard.
Related calculators
Textbook machine-design formulas (Shigley, Roark, Eurocode 3 / VDI conventions) with idealised assumptions. Use manufacturer data, material certificates and a qualified engineer's check for anything safety-related.