About the Bolt Length Calculator
Correct bolt length for a stack of parts, washers and a nut, rounded to a standard length.
Also known as: screw length calculator, how long a bolt do i need, fastener length, grip length.
How to use this calculator
- Enter total thickness of the parts, washer thickness (total), nut height, threads protruding past the nut and the other fields.
- The result updates instantly as you type — press Calculate (or Enter) at any time.
- Review the breakdown shown under the main result.
- Use Copy result or Share to save the answer or send a link with your inputs.
Formula
length = parts + washers + nut height + protrusion
Worked example
Using the values pre-filled in the calculator above:
- Total thickness of the parts = 25 mm
- Washer thickness (total) = 4 mm
- Nut height = 8 mm
- Threads protruding past the nut = 3 mm
- Thread pitch = 1.5 mm
the calculator returns:
- Standard bolt length: 40 mm
- Calculated minimum: 40 mm
- Grip length: 29 mm
- Threads showing with that length: 3 mm