Metric Bolt Size Calculator (VDI 2230 Rough Estimation)

Bolted joint is a type of joint where minimum two parts are connected to each other with a bolt. Main functions of a bolted joint are keeping parts together during service life and transmitting torque, moment and force between parts. Bolt sizing is very critical issue and improper design of a joint can lead failures.

Metric bolt size calculator roughly determines bolt diameter in a bolted joint according to guideline VDI 2230 Part-1 , which was prepared by the Association of German Engineers (VDI), and treats the calculation of concentrically and eccentrically clamped bolted joints.

This calculator can be used for initial sizing of a bolt and preload in a joint according to metric unit system. The tool is applicable for:

• Bolt dimension range from M3 to M39
• Bolt strength grades of G8.8, G10.9 and G12.9
• Axial and transverse loading
• Concentric/eccentric and static/dynamic axial loading

A sample example about bolt sizing for pressure vessel cap is given in  "Examples" section of this page to show usage of the calculation tool. Reference information on friction coefficients, load introduction factor and loading types are given in "Supplements" section to assist the usage of the calculator.

This calculator can be used to roughly estimate bolt diameter for a joint but more detailed calculation shall be done according to VDI 2230 Part-1 guideline.

Metric Bolt Sizing Calculator

Note 1 : This calculator is applicable for bolt dimension range from M3 to M39 and for strength grades G8.8 , G10.9,  G12.9.

Note 2 : Use dot "." as decimal separator.

Definitions

Axial load

Force parallel to the bolt axis. It may be concentric (through the axis) or eccentric (offset from the axis), which increases the required preload.

Transverse load

Force perpendicular to the bolt axis that tends to make clamped parts slip relative to each other. The ability to resist it depends on preload and the friction coefficient at the interface.

Preload (F_M)

The intentional tensile force applied to a bolt during tightening. Adequate preload keeps joint surfaces in contact, limits separation under service loads, and enables frictional transfer of shear.

Required preload (F_Mmax)

The design value of preload determined by the calculator after applying VDI 2230 step rules for load case and tightening method.

Bolt strength grade

Designation (e.g., 8.8, 10.9, 12.9) indicating nominal tensile and yield strengths per ISO metric fasteners. Higher grades allow smaller diameters for the same load—within the calculator’s limits.

Friction coefficient (μ)

Static friction at the interface between clamped parts. Lower μ reduces transverse load capacity for a given preload and may increase the required preload.

Tightening technique

The method used to apply preload (e.g., simple spindle, torque wrench, angle control). VDI 2230 assigns different scatter allowances; the calculator accounts for these by step increases.

Scope & limitations

This tool provides a rough VDI 2230 Part-1 based estimate for metric bolts M3–M39 in grades 8.8, 10.9, and 12.9 under axial and/or transverse loading. Final sizing requires a full VDI 2230 calculation and verification for the specific joint geometry, materials, and conditions.

General Information

Calculation methodology of the calculator is summarized below. [Reference-1]

Procedure for Selecting a Bolt (VDI 2230 – Rough Estimation)

1. Determine the governing load F.
   If only one load exists, set F = F_Amax (axial) or F_Qmax (transverse).
   If both loads exist, compare F_Amax with F_Qmax/μ_Tmin:
   – If F_Amax < F_Qmax/μ_Tmin, set F = F_Qmax (shear-controlled).
   – Otherwise, set F = F_Amax (axial-controlled).
2. Round F up to the first larger table value.
   From the “Load (N)” column, select the closest larger value than F. This becomes the new F.
3. Find F_Mmin by applying load-case steps (per VDI 2230).
   Increase the table index from Step 2 as follows:
   – If F = F_Qmax (shear-controlled): increase by 4 steps.
   – If F = F_Amax (axial-controlled):
     • Dynamic & Eccentric: +2 steps
     • Dynamic & Concentric: +1 step
     • Static & Eccentric: +1 step
     • Static & Concentric: +0 steps
4. Find F_Mmax by applying tightening-method steps.
   From F_Mmin, increase the table index by:
   – Simple tightening spindle (retightening torque): +2 steps
   – Torque wrench / precision spindle (dynamic torque or bolt elongation): +1 step
   – Angle control in plastic range or yield-point monitoring: +0 steps
5. Select the bolt at F_Mmax.
   On the row corresponding to F_Mmax, read the required nominal diameter under the chosen strength grade (12.9 / 10.9 / 8.8).

Load–Bolt Size Table

Note: Increase 1 step means, getting the value which is next row under the current value. For example if current value is 1000 N, 1 step increase will result 1600 N.

Supplements

AXIAL LOADING TYPES
Dynamic and Concentric Axial Loading
Dynamic and Eccentric Axial Loading
Static and Concentric Axial Loading
Static and Eccentric Axial Loading

Examples

Reference:

• VDI 2230 Part-1 : Systematic calculation of high duty bolted joints - Joints with one cylindrical bolt