What is the tensile stress area of a bolt?

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. It is defined in ISO 898-1 and depends on the pitch diameter and minor diameter of the thread.

How is bolt tensile strength calculated?

Bolt ultimate tensile load is calculated as Ft = Rm × As, where Rm is the ultimate tensile strength of the bolt material (determined by property class) and As is the tensile stress area. For example, a class 8.8 bolt has Rm = 800 MPa.

What does bolt property class 8.8 mean?

The first number (8) represents 1/100th of the minimum ultimate tensile strength in MPa (800 MPa). The second number (8) represents 10× the ratio of yield strength to ultimate tensile strength (0.8). So yield = 800 × 0.8 = 640 MPa.

How is bolt shear strength calculated?

Bolt shear strength is typically taken as 60% of the tensile strength: Fs = 0.6 × Rm × As. This is an engineering approximation based on the von Mises yield criterion. For single shear, use one stress area; for double shear, multiply by 2.

What is the difference between proof load and tensile strength?

Proof load is the maximum force a bolt can withstand without permanent deformation (elastic limit). Ultimate tensile strength is the maximum force before fracture. The proof load stress (Sp) is approximately 90% of the yield strength for most property classes.

Free Engineering Tool

Bolt Tensile & Shear Strength Calculator

Calculate the ultimate tensile load and shear capacity of metric bolts per ISO 898-1. Select bolt size and property class.

ISO 898-1 M3 – M64 Class 4.6 – 12.9

Bolt Size

Property Class

Shear Planes

Quick presets

Results

Ultimate Tensile Load (Ft)

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Shear Capacity (Fs)

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Tensile Stress Area (As)

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Yield Load (Fy)

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Ultimate Tensile Strength (Rm)

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Ultimate Tensile Load

The maximum tensile force a bolt can sustain before fracture:

R_m — ultimate tensile strength (MPa), from property class
A_s — tensile stress area (mm²), from ISO 898-1 / ISO 261

Shear Capacity

Bolt shear strength is approximately 60% of tensile strength (von Mises criterion):

For double shear, multiply by 2 (two shear planes).

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

Example — M10 × 8.8 Bolt

Given: M10 bolt, property class 8.8, single shear

A_s = 58.0 mm², R_m = 800 MPa

F_t = 800 × 58.0 = 46,400 N = 46.4 kN

F_s = 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.

Bolt Tensile & Shear Strength Calculator | ISO 898-1 | Free Online Tool

Published by admin on February 15, 2026 February 15, 2026

Results

Ultimate Tensile Load

Shear Capacity

Property Classes per ISO 898-1

Practical Example