Bolt Shear Strength Calculator | Single & Double Shear (AISC, Eurocode, ISO)

Bolt shear strength is the maximum lateral (sideways) force a bolt can resist before fracturing across its cross-section — as if the bolt is being cut like a pair of scissors. Tensile strength (Fu) is the maximum axial (along the bolt axis) pulling force it can resist before breaking.

These are distinct mechanical properties. Shear strength is approximately 0.577 to 0.60 times the ultimate tensile strength for ductile steel bolts (Von Mises criterion). For example, a bolt with Fu = 830 MPa has a shear strength of approximately 479–498 MPa.

This calculator addresses shear failure only. It is not a torque calculator, clamping force calculator, or preload tool — those all deal with axial tension.

The fundamental approach for calculating bolt shear strength by hand:

• Step 1: Find the shear area. If threads are in the shear plane: \(A_t = \frac{\pi}{4}(d - 0.9382P)^2\). If shank: \(A = \frac{\pi d^2}{4}\)
• Step 2: Find allowable shear stress: \(\tau_{allow} = \frac{0.577 \times F_u}{SF}\) where SF is your safety factor
• Step 3: Allowable capacity = \(\tau_{allow} \times A \times n_{planes} \times n_{bolts}\)
• Step 4: Compare with applied force. If capacity > applied → safe

The calculator automates all four steps and handles unit conversions, grade lookups, and code factors automatically.

Single shear occurs when two plates overlap and a bolt connects them — there is one cut plane. The full applied force is resisted at one cross-section of the bolt.

Double shear occurs in a three-plate (clevis-type) connection where the middle plate is sandwiched between two outer plates. The bolt has two cut planes, so the applied force is split between two cross-sections. This approximately doubles the shear capacity for the same bolt size and grade.

For example: an M16 Grade 8.8 bolt might carry 30 kN in single shear but 60 kN in double shear. Always confirm which configuration your joint uses before selecting single or double in the calculator.

It depends on where the shear plane intersects the bolt:

• Use tensile stress area (\(A_t\)) — conservative: When threads pass through the shear plane. Required by AISC 360 for standard connections unless otherwise verified. About 75–80% of gross area.
• Use gross shank area (\(A_{shank}\)) — optimistic: Only when the shear plane is verified to pass through the unthreaded shank. Applicable for shoulder bolts or when grip length is specifically controlled.

When in doubt, always use the threaded (tensile stress) area. This is the default in the calculator and the most structurally conservative assumption.

ASTM A325 bolts have an ultimate tensile strength Fu = 120 ksi (830 MPa). The shear strength is:

• Ultimate shear strength: ≈ 0.577 × 120 = 69.2 ksi (477 MPa)
• AISC 360 Nominal F_nv: 54 ksi (372 MPa) with threads in shear plane; 67.5 ksi (465 MPa) with threads excluded
• LRFD design shear (\(\phi R_n\)): Use \(\phi = 0.75\) applied to \(R_n = F_{nv} \cdot A_b\)

Use the Grade dropdown in the calculator to auto-fill A325 values and get the full capacity for your specific diameter, configuration, and code.

Safety factor depends on the applicable design standard and application:

• AISC 360 LRFD: Use resistance factor \(\phi = 0.75\) (equivalent SF ≈ 2.0 for typical load combos)
• AISC 360 ASD: Safety factor \(\Omega = 2.00\)
• Eurocode 3: Partial factor \(\gamma_{M2} = 1.25\)
• ISO 898 / machine design: SF = 1.5 to 3.0 depending on consequence of failure
• ASME pressure vessel: SF = 3.0 (conservative, safety-critical)

Higher safety factors are used for shock loads, fatigue-prone applications, or connections where failure could cause injury. The calculator lets you set a custom factor if your project specification requires one.

Shear force acts perpendicular (transverse) to the bolt axis — it tries to cut the bolt sideways. A bolt in shear acts like a pin resisting two plates from sliding apart.

Tensile force (preload) acts along the bolt axis — it stretches the bolt and creates clamping force between plates. Torque is the rotational force applied to generate this preload.

These are completely different structural problems. This calculator handles shear only. For preload and torque calculations, use a separate Torque → Clamping Force Calculator. If both forces act simultaneously, run the combined shear + tension interaction check (Formula 9 in this guide).

The utilization ratio is the ratio of the applied shear force to the total allowable shear capacity, expressed as a percentage:

\(\text{Utilization} = \frac{F_{applied}}{F_{allow}^{total}} \times 100\%\)

• Below 80%: Safe with adequate margin (green)
• 80–100%: Near limit — the bolt is close to its capacity. Review the design (amber)
• Above 100%: Failure — the applied load exceeds allowable capacity (red)

A utilization of 60–75% is typical for well-designed connections that leave margin for load uncertainty and fatigue.

Bearing failure occurs when the bolt crushes or elongates the hole in the connected plate, rather than the bolt body shearing. This happens when the plate material is weaker or thinner than the bolt itself.

Bearing capacity (AISC): \(R_n = 2.4 \cdot F_{u,plate} \cdot d \cdot t\). If this value is less than the bolt shear capacity, bearing governs the design.

When to check: Always check bearing when using thin plates (<10 mm), low-grade plate material (e.g., A36 at 400 MPa), or high-strength bolts (A490, 10.9) in thin connections. Use the Advanced → Bearing Check tab in the calculator.

Yes — the formula reference in this guide (Formulas 1–10) can be directly replicated in Microsoft Excel or Google Sheets. The key Excel formulas are:

• Shank area: =PI()/4*d^2
• Tensile stress area: =PI()/4*(d-0.9382*P)^2
• Allowable shear stress: =0.577*Fu/SF
• Shear capacity: =tau_allow*A*n_planes*n_bolts
• Utilization: =F_applied/F_capacity*100

Use the Export / Copy tab in the calculator to copy a fully formatted plain-text report of any calculation to paste into your Excel workbook or engineering log.