The hardest part of most calculations is not the maths — it is finding a tool you can trust. Think of the bolt weight calculator as a second opinion you can get in seconds.
Nothing you type here leaves your browser. That is why the full formula is printed below, variable by variable.
What this tool measures
On technical fasteners errors are paid in real time: too little torque means a loose joint; too much means stripped threads or a cracked head. How this calculation applies in United Kingdom:
Bolt weight online calculator turns bolt, screw and nut specs into concrete numbers — torque, shear load, preload, weight. 10.9 is 25% stronger tensile and used in preloaded joints (structural steel, engines). For repeatedly disassembled joints — use self-locking nuts or spring washers.
For M10 8.8 that's about 47 Nm dry, ~35 Nm lubricated.
Behind the calculate button
Most ordinary: using one torque value for dry and lubricated joints (25% error). Re-check torque after 24 hours (preload drops 5–10% on first loading). Second: ignoring property class — 4.6 and 12.9 need very different torque at the same diameter.
Third: over-tightening stainless — A2/A4 have 60–70% the strength of class 8.8 steel. Never increase torque to compensate for loosening — replace the fastener.
For critical joints use a torque wrench with ±4% accuracy.
The equation, decoded
Bolt weight online calculator applies the right constants for the property class (8.8, 10.9, 12.9, A2-70, A4-80). Figures here follow UK conventions — pounds, imperial-metric mix and HMRC defaults where applicable. It builds on ISO 898 and DIN 933/931 plus the classic T = K × D × F equation (T — torque in Nm, K — friction coefficient 0.15–0.20, D — nominal diameter in m, F — preload in N).
Weight uses volume × material density (steel 7.85 g/cm³, stainless 7.95, brass 8.5, aluminium 2.7, titanium 4.5). That means the output can be used directly with an accountant, lender or employer in the UK without converting anything. The number pair encodes tensile strength (8.8 = 800 MPa tensile, 640 MPa yield).
When this page is worth a visit
Use 931 for shear joints, 933 for tension. DIN 931 (ISO 4014) — partial thread (plain shank under the head).
Down-substitution risks shear failure or loosening. DIN 933 (ISO 4017) — fully threaded. Only with designer approval.
Situations this was built for
- Local notes: Figures here follow UK conventions — pounds, imperial-metric mix and HMRC defaults where relevant.
- VAT / sales tax: Standard UK VAT is 20%; reduced 5% for domestic energy and children's car seats; 0% for most food, books and children's clothes. VAT registration is compulsory above £90,000 turnover (2024/25).
- Electrical supply: Mains is 230 V / 50 Hz, Type G plug (three rectangular pins with fuse). Ring-main circuits typically 32 A.
- Units of quantify: Mixed system: distances in miles, speed limits in mph, but food/fuel in litres and kg. Beer in pints, milk frequently in pints. Weight of a person commonly quoted in stones (1 stone = 14 lb ≈ 6.35 kg).
- Currency & format: Pound sterling (GBP, £). Thousands separator is comma, decimal is a dot.
Practical tips
The figures below reflect current UK practice, so Bolt weight calculator can be used without converting anything by hand. Steel: 4.6, 5.6, 8.8, 10.9, 12.9.
Every figure above applies to United Kingdom specifically and is reviewed when the rules change. Stainless: A2-70, A4-70, A4-80.
Mistakes worth dodging
Recalculate after changing one input at a time; this presents which assumption controls the answer and makes an unexpected answer easier to diagnose. The values entered here are Nominal diameter (mm), Shank length (mm), Material. For the United Kingdom, use the units printed beside each field and do not assume that a familiar name means the same measurement system. Fasteners look simple but are critical on load-bearing assemblies.
A closing note
The difference between a good and a bad move is often a single computed figure. If the figure surprised you, run it again with the conservative version of your inputs and see what survives.
the United Kingdom-specific questions
Is this Bolt weight calculator valid for the United Kingdom?
Yes. It uses pound sterling (GBP, £) and mixed (miles & mph, litres & kg, stones), and any tax or contribution reference follows HMRC rules.
Which units and number format are used?
Amounts display as £1,234.56 and quantities in mixed (miles & mph, litres & kg, stones) — the official convention in the UK.
Which pension and tax model is assumed?
State Pension + workplace auto-enrolment. The tax framework is income tax 20/40/45%, VAT 20%.