Bolt & Nut Weight Calculator

How Bolt Weight Is Calculated

Unlike round bars or plates, bolt weight cannot be calculated using simple volume × density formulas. The hex head geometry, thread pitch, and shank diameter all affect the final weight. The threaded portion is lighter than a solid cylinder of the same diameter because material is removed during thread cutting, and the hex head adds concentrated mass at one end.

This calculator works from the nominal dimensions in the standards: hex head size from ISO 4014/4017 (IS 1364 in India), nut size from ISO 4032, and plain washer size from ISO 7089. Bolt weight = hex head volume + shank volume (π/4 × d² × length), with small allowances for chamfers and thread loss. Only the shank grows with length — the head stays the same — so doubling the length does not double the weight. Results are typically within about ±10% of manufacturer catalogue weights.

For accurate BOM (Bill of Material) and procurement estimates, prefer the manufacturer's weight table where available. Property class (4.6, 8.8, 10.9) does not change weight. DIN 931/933 bolts use a larger across-flats size for M10 (17mm) and M12 (19mm) than ISO (16mm and 18mm), so DIN parts of those sizes are slightly heavier.

Worked Example — M16 × 75mm Bolt Set (100 Pieces)

For a steel structure connection requiring 100 sets of M16 × 75mm hex bolts with nuts and washers:

• Hex head (24mm A/F × 10mm high) ≈ 0.037 kg
• Shank = π/4 × 16² × 75mm × 7.85×10⁻⁶ (less ~3% for threads) ≈ 0.115 kg
• M16 × 75 bolt ≈ 0.152 kg
• M16 hex nut (ISO 4032) ≈ 0.0375 kg; M16 plain washer (ISO 7089, 17/30/3mm) ≈ 0.0113 kg
• Total per set ≈ 0.152 + 0.0375 + 0.0113 = 0.201 kg
• 100 sets ≈ 20.1 kg

Metric Bolt, Nut & Washer Weight Chart — M6 to M36

Approximate hex bolt weight at 50mm length, hex nut and plain washer weight for M6 to M36 in carbon steel, calculated from ISO 4017 / ISO 4032 / ISO 7089 nominal dimensions. For other lengths, use the calculator above — only the shank part changes with length.

Note: Calculated nominal weights (±10% vs catalogues) for hex head bolts. Socket head cap screws (Allen bolts) have different weights due to the cylindrical head shape. U-bolt weights depend on the bend radius and cannot be derived from this table — see the FAQ below.

When Do You Need Bolt Weight Calculation?

Bolt weight calculation is essential in several engineering and procurement scenarios. During material indenting, suppliers often quote fasteners by weight rather than per piece — knowing the total weight helps verify invoices and prevent over-ordering or short supply.

In structural steel fabrication, the BOM for a steel building or bridge includes fastener weights for transportation planning and crane capacity calculations. A typical steel building connection might use 500–2,000 high-strength bolts, and their combined weight can reach 200–800 kg — significant enough to affect logistics and rigging plans.

For shipping and freight estimation, particularly in export orders, the total consignment weight including fasteners determines the freight cost. Missing even 50 kg of bolt weight in a 10-tonne shipment can cause billing discrepancies at the weighbridge.