Free Engineering Tool
Bolt Tensile & Shear Strength Calculator
Calculate the ultimate tensile load of metric bolts from ISO 898-1 property-class data, plus a simplified shear capacity estimate. Select bolt size and property class.
This calculator was developed and verified by the Vibromera engineering team, makers of the Balanset portable balancing instruments.
Results
Ultimate Tensile Load
The maximum tensile force a bolt can sustain before fracture:
- Rm — ultimate tensile strength (MPa), from property class
- As — tensile stress area (mm²), from ISO 898-1 / ISO 261
Shear Capacity (Simplified Estimate)
ISO 898-1 defines the tensile and proof-load properties of bolts — it does not specify shear strength. The value shown here is a widely used simplified engineering estimate that takes shear strength as approximately 60% of tensile strength (based on the von Mises criterion, τ ≈ 0.58 σ):
For double shear, multiply by 2 (two shear planes).
⚠️ Shear design note: Actual shear capacity depends on whether the shear plane passes through the threads or the unthreaded shank, on joint slip and plate bearing, and on fatigue loading. Design codes define their own values — e.g. Eurocode 3 (EN 1993-1-8) uses Fv = αv × fub × A with αv = 0.6 for classes 4.6, 5.6 and 8.8 but 0.5 for classes 4.8, 5.8, 6.8 and 10.9, together with partial safety factors. Always verify shear-loaded joints against the applicable structural or mechanical design code, not this simplified estimate alone.
Property Classes per ISO 898-1
| Class | Rm (MPa) | Rp0.2 (MPa) | Typical Use |
|---|---|---|---|
| 4.6 | 400 | 240 | Low-strength, general purpose |
| 5.8 | 520 | 420 | Structural, non-preloaded |
| 8.8 | 800 | 640 | Automotive, machinery (most common) |
| 10.9 | 1040 | 940 | High-strength structural |
| 12.9 | 1220 | 1100 | Maximum strength (alloy steel) |
Practical Example
Given: M10 bolt, property class 8.8, single shear
As = 58.0 mm², Rm = 800 MPa
Ft = 800 × 58.0 = 46,400 N = 46.4 kN
Fs = 0.6 × 800 × 58.0 = 27,840 N = 27.8 kN
⚠️ Note: These are ultimate capacities without safety factors. Apply appropriate safety factors (typically 2–3 for static, 4–6 for fatigue) for design purposes.
The tensile stress area (As) is the effective cross-sectional area used to calculate the tensile load capacity of a threaded fastener. It is smaller than the nominal shank area because it accounts for the thread root geometry. Values are tabulated in ISO 898-1.
Ultimate tensile load is Ft = Rm × As, where Rm is the ultimate tensile strength (from the property class) and As is the tensile stress area. For example, a class 8.8 bolt has Rm = 800 MPa.
The first number (8) represents 1/100th of the minimum ultimate tensile strength in MPa (800 MPa). The second number (8) is 10× the ratio of yield to ultimate strength (0.8). So yield ≈ 800 × 0.8 = 640 MPa.
ISO 898-1 does not specify shear strength — it covers tensile and proof-load properties only. A common simplified estimate takes shear strength as 60% of tensile strength: Fs = 0.6 × Rm × As, based on the von Mises yield criterion. Design codes such as Eurocode 3 (EN 1993-1-8) apply their own factors (0.6 or 0.5 depending on property class) plus safety factors. For double shear (two planes), multiply by 2.
Proof load is the maximum force without permanent deformation (elastic limit). Ultimate tensile strength is the maximum force before fracture. Proof load stress is approximately 90% of yield strength for most property classes.
The procedures described on this page were developed and field-tested by the Vibromera team using the Balanset-1A, a portable dual-channel balancer and vibration analyzer for on-site rotor balancing.
Professional field balancing instruments and software. Used in 50+ countries.
