Calculator
Enter factored actions and bolt details. The tool estimates minimum bolt quantity and suggests a practical grid.
Formula used
The calculator estimates bolt design capacities using typical strength values and practical reduction factors. It then divides the factored action by per-bolt resistance and rounds up.
- Ab = π d² / 4 (bolt shank area, mm²)
- Vn = 0.6 fu Ab np R (nominal shear, N)
- Vd = φV Vn / 1000 (design shear, kN)
- Tn = 0.75 fu Ab (nominal tension, N)
- Td = φT Tn / 1000 (design tension, kN)
- Required bolts:
- Shear: n = ceil(V / Vd)
- Tension: n = ceil(T / Td)
- Combined: n = ceil( √[(V/Vd)² + (T/Td)²] )
R is a product of reduction factors for threads, hole type, and connection type.
How to use this calculator
- Choose the load mode that matches your connection forces.
- Enter factored shear V and/or factored tension T in kN.
- Select bolt diameter, grade, shear planes, and detailing options.
- Set resistance factors used in your design workflow.
- Optionally enable geometry check to ensure a grid fits.
- Click Calculate to see results above the form.
- Download CSV or PDF for documentation and sharing.
This estimator does not replace code-based connection design checks such as bearing, tear-out, block shear,
prying action, slip resistance, and plate thickness limits.
Example data table
Sample inputs and typical output to help you verify the workflow.
| Case | Mode | V (kN) | T (kN) | Bolt | Planes | Threads | Hole | φV / φT | Result (n) |
|---|---|---|---|---|---|---|---|---|---|
| A | Shear | 120 | 0 | M20 Grade 8.8 | 1 | Yes | Standard | 0.75 / 0.75 | 2–3 (depends on options) |
| B | Combined | 80 | 60 | M16 Grade 10.9 | 1 | No | Standard | 0.75 / 0.75 | 2–4 (depends on interaction) |
| C | Tension | 0 | 150 | M24 Grade 8.8 | — | — | Standard | 0.75 / 0.75 | 2–3 (depends on options) |
Tip: If the suggested layout status shows exceeds, increase plate size or reduce spacing.