Bolt Weight Calculator

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Theoretical weight of hexagon head bolts in carbon and alloy steel. Pick the standard and size, enter the length, and the calculator returns weight per piece, per 100 pieces and for your full quantity — with the head, shank and thread volumes shown separately.

Use your own for drawing parts or non-standard heads.
Ordinary hex bolt, coarse thread.
Square heads weigh about 15% more.
Measured across the flats, not the corners.
Nominal, or the turned shank on a fit bolt.
Coarse pitch unless the drawing says otherwise.
Under the head, to the point.
Thread length calculated from the standard.
From your drawing or the standard.
Head + rod, less 4% when partly threaded.
For the total line weight.
g/cm³

—kg per piece
—kg per 100 pcs
—kg total
Head — Plain shank — Threaded part — Thread length used — Across flats — Head height —

Theoretical weight from nominal dimensions. Actual weight normally runs 2–3% higher because of the under-head radius, chamfers and thread tolerances. Use it for costing and freight estimates, not for weighing acceptance.

Please read before you quote. These are theoretical weights from nominal dimensions. Actual weight normally comes out 2–3% higher, because the under-head radius, the chamfer and thread tolerances all add metal the formula does not account for. Use the figures for costing, packing and freight estimates. For contract quantities, confirm against a weighed sample.

Weight chart — kg per 100 pieces

ISO 4014 partly threaded hex bolts, property class 8.8, carbon steel at 7.85 g/cm³.

How this is calculated

Weight is the sum of three volumes multiplied by the material density:

  • Head — a hexagonal prism: 0.866 × s² × k, where s is the width across flats and k the head height.
  • Plain shank — a cylinder at nominal diameter: π/4 × d² × (L − b).
  • Threaded portion — a cylinder at the pitch diameter: π/4 × d₂² × b, where d₂ = d − 0.6495 × p and p is the thread pitch.

Pitch diameter is used for the threaded length because the thread crests and roots roughly balance around it, so it represents the metal actually present. Nominal diameter overstates the weight; minor diameter understates it.

Thread length for partly threaded bolts follows ISO 888: b = 2d + 6 up to 125 mm length, 2d + 12 over 125 to 200 mm, and 2d + 25 above 200 mm.

Trade method. The shop-floor calculation used across the fastener trade: head plus the full rod at nominal diameter, recalculated at pitch diameter when the bolt is fully threaded, or with a flat 4% taken off the rod when it is partly threaded. It is quicker, needs no thread length, and because theoretical figures normally fall 2–3% below actual weight, the 4% allowance tends to land closer to the weighbridge than the exact split does.

Both methods are shown together, so you can see the gap on any given size before you quote.

Need these bolts manufactured, or a weight confirmed against a drawing? S R Forgings manufactures hexagon and structural bolts in Ludhiana, in property classes 4.6 to 12.9, black, hot-dip galvanised or zinc flake coated.

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