# Bolt Capacity Calculator

Shear or bearing, whichever is lower, governs — above 9 mm plate it is usually shear.

- Page: https://jianzhujisuan.com/en/bolt-capacity
- Category: Structural Design (https://jianzhujisuan.com/en/c/structural-design)
- Chinese version: https://jianzhujisuan.com/zh/bolt-capacity.md
- Data checked: 2026-10-25

## Quick result

With the default inputs (Bolt diameter d 20 mm, Bolt grade Grade 8.8, Bolt tensile strength fub 800 MPa, Plate tensile strength fu 430 MPa, Plate thickness t 10 mm, Edge distance e 40 mm, Bolt pitch p 60 mm, Shear planes 1, Number of bolts 6): **Design resistance per bolt 94.0 kN**

## Inputs

| Parameter | Type | Default | Unit | Note |
|---|---|---|---|---|
| Bolt diameter d | number | 20 | mm |  |
| Bolt grade | select | Grade 8.8 | — |  |
| Bolt tensile strength fub | number | 800 | MPa |  |
| Plate tensile strength fu | number | 430 | MPa |  |
| Plate thickness t | number | 10 | mm |  |
| Edge distance e | number | 40 | mm |  |
| Bolt pitch p | number | 60 | mm |  |
| Shear planes | number | 1 | — |  |
| Number of bolts | number | 6 | — |  |

## Formula

- **Shear area (threads)**: As = π/4·(d − 0.9382P)²　M20 P=2.5 → 245 mm²
- **Shear resistance**: Fv,Rd = αv·fub·A/γM2
- **αv (grades 4.6, 8.8)**: 0.6
- **αv (grade 10.9)**: 0.5
- **Bearing factor**: αb = min(e/3d0, p/3d0 − 0.25, fub/fu, 1.0)
- **Bearing resistance**: Fb,Rd = 2.5·αb·fu·d·t/γM2
- **Group**: N = min(Fv,Rd, Fb,Rd) × n

## Worked example

M20 grade 8.8 at fub 800, plate fu 430, 10 mm thick, 40 mm edge, 60 mm pitch, single shear, six bolts: stress area 245 mm², 94.1 kN in shear, 22 mm hole, αb 0.606, 104.2 kN bearing — shear governs, 94.1 kN per bolt and 565 kN for the group.

## Questions

### How much load can one bolt take?

Check shear and bearing and take the lower. An M20 grade 8.8 in single shear gives 94 kN in shear using the threaded stress area of 245 mm², not the gross 314; against a 10 mm plate with 40 mm edge distance bearing is 104 kN, so 94 kN is the working figure. Above about 9 mm plate shear governs; only thin plates crush the hole first. Using the gross area for shear is the classic error and overstates by 28%.

### What is the difference between high strength and ordinary bolts?

It is the load path, not the steel. Ordinary bolts transfer load through the shank in shear and the hole in bearing, and the joint slips before it works. Friction grip high strength bolts are pre-tensioned so the plates are clamped and load crosses by friction — no slip, better fatigue, but they need a torque wrench and a final tightening check. This tool computes the shear and bearing (bearing type) case; the friction grip resistance is mu n 0.7 fub A / 1.25, with mu about 0.5 for grit blasted and 0.3 for painted surfaces, usually lower than bearing type — you trade capacity for no slip. Use friction grip wherever the load reverses or fatigues.

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