Bolt Weight Calculator
Calculate the weight of a steel bolt from its diameter and length, using standard steel density.
How this calculator works
A bolt’s weight comes down to how much steel is packed into its shape. This calculator treats the bolt’s shank as a simple cylinder, calculates that cylinder’s volume from the diameter and length, and multiplies by the standard density of steel to get a weight in pounds.
The volume calculation uses the bolt’s radius, which is half the diameter, squared and multiplied by pi and the length. That volume, in cubic inches, is then converted to weight using steel’s density of 0.284 lb per cubic inch.
Formula: Weight = cylinder volume (π × radius² × length) × steel density (0.284 lb per cubic inch).
Worked example
A 0.5-inch diameter bolt, 3 inches long:
- Diameter: 0.5 in (radius 0.25 in)
- Length: 3 in
- Volume: π × 0.25² × 3 ≈ 0.589 in³
- Weight: 0.589 × 0.284 ≈ 0.167 lb
Notes
This calculator treats the bolt as a plain cylinder, which is really just the shank of the bolt. That approach slightly overestimates the true weight, since real bolts have threads cut into part of their length, and cutting threads removes material. A bolt head adds some weight back, but usually not enough to fully cancel out the overestimate from the threads.
For most practical purposes, this is close enough. It works well for shipping weight estimates and bulk-order planning, where being off by a small margin doesn’t change the outcome. It is not precise enough for a scale-critical application, where every fraction of a pound matters.
For the exact figure, use the fastener manufacturer’s published weight per 100 or per 1,000 pieces. Those figures come from actual measured bolts, including the real thread and head geometry, rather than a cylinder approximation.
How to use
Enter the bolt’s diameter and length in inches. The calculator works out the cylinder volume and multiplies it by standard steel density to give an estimated weight in pounds, useful for quick shipping or bulk-order planning.
This is a planning estimate using standard mechanical engineering formulas, not a substitute for engineering design. Confirm actual fastener sizing and torque specs with the fastener manufacturer or a structural engineer.
Frequently asked questions
Why does this calculator treat a bolt as a plain cylinder?
Treating the bolt as a simple cylinder, using its diameter and length, makes the math straightforward and gives a close estimate without needing detailed thread geometry. Real bolts have threads that remove some material and a head that adds a bit back, but for most planning purposes the cylinder approximation is close enough.
Does this estimate run high or low compared to the real weight?
It tends to run slightly high, since it doesn't subtract the material removed by threading. The head does add some weight back, but that usually doesn't fully offset the overestimate from ignoring the threads. For shipping and bulk-order planning, that small overestimate is generally not a problem.
Where does the 0.284 lb per cubic inch figure come from?
That figure is the standard density of steel, used to convert a calculated volume into a weight. It applies to typical carbon steel fasteners. Other materials, like stainless steel or brass, have different densities, so this calculator's result is specific to steel bolts.
When should I use the manufacturer's published weight instead?
Use the manufacturer's published weight per 100 or per 1,000 pieces whenever precision matters, such as for scale-critical shipping calculations or exact material orders. This calculator's cylinder-based estimate is meant for quick planning and bulk estimates, not for applications where the exact figure is required.
Estimates only. Verify quantities with your supplier before purchasing.