How do I calculate the carbon footprint of bolts, nuts and screws per kg?
Multiply the wire rod used per kg of fasteners, including scrap, by your steel supplier's factor. Add wire drawing, cold heading, thread rolling and heat treatment energy, then zinc plating or coating. Divide by kilograms dispatched. Steel is usually most of the total; heat treatment is next.
Steel
- Wire rod or bar bought per kg sold, including heading and trimming scrap.
- Get a per-tonne figure from the mill; blast furnace, DRI and scrap EAF routes differ widely.
- If you export to the EU, fasteners under CN 7318 are CBAM goods, so the importer needs embedded emissions data.
Processing
- Annealing and hardening furnaces: electricity, PNG or LPG, plus endothermic gas.
- Cold heading and thread rolling machines.
- Pickling, phosphating and zinc or zinc-flake coating lines.
Per kg
Divide by kilograms of finished product packed and sold, not by raw material bought.
Worked example: fastener plant per kg (one month)
- Electricity: 150,000 kWh x 0.710 = 106,500 kg CO2
- Hardening furnace PNG: 20,000 SCM x 2.05 = 41,000 kg CO2
- Fasteners dispatched (kg): 300,000
- Plant total: 147,500 / 300,000 = 0.492 kg CO2 per kg
- Add wire rod at your mill's factor for the full figure
Inputs are illustrative; use your own bills and production records.
What Senseible does here
Senseible reads the plant's electricity bills (CEA grid factor 0.710 kg CO2 per kWh, CO2 Baseline Database version 21.0) and fuel invoices (IPCC 2006 defaults) into a fingerprinted Scope 1 and 2 record, the plant-level input to a per-unit figure. Bought-in materials go to the supplier evidence trail; product reports are self-declared drafts.
- Product carbon footprint calculator
- Are nuts and bolts covered by CBAM?
- CBAM for fastener exporters
- Steel industry
Sources: GHG Protocol Product Standard, ISO 14067:2018, Carbon footprint of products (iso.org), IPCC 2006 Guidelines, Volume 2 Energy (fuel defaults), CEA CO2 Baseline Database, version 21.0
Last reviewed 2026-10-20.