Bolt Weight Calculator

How much does a steel bolt weigh?

A bolt weight calculator treats the bolt’s shank as a solid steel rod. Weight = π × (diameter ÷ 2)² × length × 0.284 lb per cubic inch. A ½ in diameter bolt, 3 in long, has a shank volume of 0.589 in³, so it weighs about 0.167 lb. That is roughly 16.7 lb per hundred, before heads and nuts.

Weight comes up when shipping a pallet of anchor bolts, checking that a bin will not overload a shelf, estimating the steel in a connection, or deciding how much hardware a crew can carry up a ladder.

The formula in plain words

A bolt shank is a cylinder. Its volume is the area of the round end times the length.

1. Radius = diameter ÷ 2.
2. End area = π × radius², in square inches.
3. Volume = end area × length, in cubic inches.
4. Weight = volume × 0.284, the weight of one cubic inch of steel.

Because diameter is squared, it drives weight far more than length. Going from ½ in to 1 in diameter makes a bolt four times heavier. Doubling the length only doubles it.

Worked examples

1. Calculator defaults: ½ in diameter, 3 in long

• Radius: 0.5 ÷ 2 = 0.25 in
• End area: π × 0.25² = 0.196 in²
• Volume: 0.196 × 3 = 0.589 in³
• Weight: 0.589 × 0.284 = 0.167 lb

2. A box of 100 anchor bolts, ¾ in × 6 in

• Radius: 0.375 in
• Volume: π × 0.375² × 6 = 2.651 in³
• Weight per bolt: 2.651 × 0.284 = 0.753 lb
• Per 100: 0.753 × 100 = 75.3 lb of shank steel

Add the nuts and washers on top. A box that size is too heavy to pass up a ladder in one go.

Steel shank weight by diameter

Diameter	lb per inch of length	4 in long	per foot of length
¼ in	0.0139	0.056 lb	0.167 lb
⅜ in	0.0314	0.125 lb	0.376 lb
½ in	0.0558	0.223 lb	0.669 lb
⅝ in	0.0871	0.349 lb	1.046 lb
¾ in	0.1255	0.502 lb	1.506 lb
1 in	0.2231	0.892 lb	2.677 lb

The “per foot” column also works for threaded rod, which has no head. For hex-head bolts, the head adds weight that this table does not include. On a short, thick bolt the head can be a big share of the total, so short-bolt results will run low.

How to measure a bolt

• Diameter: measure the unthreaded shank with calipers, or use the nominal size. A ½-13 bolt is ½ in.
• Length: for hex bolts, measure from under the head to the tip. That is how bolt length is sold, and it matches what the calculator needs.
• Threaded rod: use the full length.
• Metric bolts: convert first. M12 is 12 ÷ 25.4 = 0.472 in; 50 mm long is 1.97 in.

Common mistakes

• Entering the diameter as a fraction. Type 0.375 for ⅜ in, not 3/8.
• Using the thread pitch as a size. In ½-13, the 13 is threads per inch, not a dimension.
• Forgetting the nuts. A heavy hex nut can weigh a good share of a short bolt, and big connections use two per bolt plus washers.
• Assuming all metals weigh the same. Aluminum bolts weigh about a third as much as steel. Stainless and brass weigh a little more.

Related structural tools

For plates, angles, and bar stock, the steel weight calculator uses the same 0.284 lb/in³ density. Reinforcing bar has its own standard weights per foot in the rebar weight calculator. Once you know which bolt you are using, set its tightening value with the bolt torque calculator, and check what it can carry with the bolt shear calculator. Weight is a planning figure; bolt grade, size, and connection design for structural work should come from the fastener manufacturer or a licensed structural engineer.