Embodied carbon and EPDs for metals

At a glance

CO₂ and CO₂e are tonnes of carbon dioxide, or carbon dioxide equivalent, per tonne of metal. The rows use different boundaries and years and must not be compared with each other.

Three questions before you use any number

A carbon figure for a metal is only as useful as its answers to three questions.

1. Which stages does it cover? The International Aluminium Institute (IAI) specifies a cradle-to-gate footprint: from raw material extraction until the product leaves the factory, including direct and indirect emissions. The steel industry’s headline indicator is per tonne of crude steel cast, which is before rolling and fabrication. A published eco-profile for steel sections adds an end-of-life recycling credit, so its figure is a net one. These are three boundaries, not one.
2. How was the metal made? The same metal differs several times over by route: scrap-based or ore-based steel, aluminium smelted with hydro or coal power, stainless made largely from scrap or with nickel pig iron. IAI says electricity is the major source of variability in primary aluminium.
3. Is it for this product, or an industry average? A global or regional average describes the industry. A product EPD, verified against a rulebook, describes one maker’s product. Most bespoke metalwork has neither, so the honest answer is often an estimate with its limits stated: see embodied carbon data for FF&E.

What the metal bodies publish

Steel. The World Steel Association’s Sustainability Indicators 2023 report (November 2023, with 2022 data) gives the global average as 1.91 tonnes of CO₂ per tonne of crude steel cast. By route it gives 2.33 for the blast furnace route, 0.68 for scrap-based electric arc furnaces and 1.37 for electric arc steel made from direct reduced iron. It says the method covers all scopes (1, 2 and some 3). That is a measure of crude steel. Worldsteel also publishes eco-profiles in the EPD style: the page for sections declares one tonne, cradle to gate with end-of-life recycling credits at a 90 % rate, as a regional (Asia) average of blast furnace and electric arc routes.

Stainless steel. The industry body worldstainless describes two production systems, scrap-based and nickel pig iron, and says at least 95 % of stainless steel is recycled at the end of its life. It reports cradle-to-gate emissions across scopes 1 to 3 but gives the detail to members only, so this sheet quotes no stainless figure. See 304 against 316 for the grades.

Aluminium. The IAI’s September 2023 guide says most cradle-to-gate footprints for primary aluminium fall in the range 4.5 to 22 tonnes of CO₂e per tonne, and that in 2023 a footprint of 4 or less is the lowest achievable at commercial scale. It warns that some declared footprints omit emissions outside the owner’s facilities or upstream of the smelter. On scrap, it says the footprint may include scrap, and that the method used for the scrap share and the shares of pre-consumer and post-consumer scrap should be disclosed. See aluminium alloys for interiors.

Copper. The International Copper Association (ICA) says recycling copper needs 85 % less energy than primary production, that 32 % of global copper demand is met with recycled copper, and that 40 % of copper is recycled at the end of a product’s life (56 % if pre-consumer scrap is added). These are industry statements for copper, not carbon footprints of brass or bronze. See brass alloys.

From a tonne to a piece

A factor per tonne becomes a figure for a piece by multiplying it by the mass. The arithmetic is simple and the result is still weak. The worldsteel factors are for crude steel, so they leave out rolling, cutting, welding, finishing and transport, and they say nothing about the route that made your steel. This table shows the effect of the route alone, for an invented 20 kg piece:

The spread, from 13.6 to 46.6 kg, is the point: the route alone changes the answer by a factor of more than three. It is a demonstration of the sum, not an assessment, and no such figure should be given to a client as the carbon of a piece.

What to ask for, and how to word a reply

Ask the supplier, in writing and before ordering, for these. Read EPDs with how to read an EPD, and see sustainability documents a tender will ask for for the wider list.

When a client asks for the carbon of the metalwork, give the figure with its source, boundary and year, or say that no figure exists. Avoid “low carbon”, “green” and “sustainable” unless a document supports the wording. A recycled-content claim needs the share, the type of scrap and the method.

This sheet does not say that Make Bespoke Studio or any partner workshop holds an EPD or a carbon figure for any metal.

For [metal and grade], the supplier to state in writing: the production route [primary / scrap-based electric arc / other], the recycled content as separate pre-consumer and post-consumer shares with the method used, and any carbon figure with its boundary [cradle to gate unless stated], year and data source. A figure without its boundary will not be accepted.

Where a product-specific environmental product declaration exists, to be supplied with its registration number, programme, declared unit, modules declared and valid-to date, verified by a named independent third party, to BS EN 15804+A2 [edition]. Where none exists, the supplier to say so in writing.

Embodied carbon of the [metalwork] [has not been calculated] [is estimated at [ ] kg CO₂e for modules [A1 to A3], from [source, edition, year], for [quantity] of [metal]. This is an estimate from generic data, not a product declaration].

Standards and sources

• World Steel Association, Sustainability Indicators 2023 report (November 2023): 2022 data; read in full.
• International Aluminium Institute, Specifiers' Guide to IAI's Carbon Footprint Methodology (September 2023): read in full.
• worldstainless, Stainless Steels and CO2; ICA, Circular Economy: web pages read 7 Nov 2026.
• BS EN 15804:2012+A2:2019: BSI listing: Current, Under Review; not read.

Questions we are asked

Which metal has the lowest embodied carbon?

No fair answer exists without a boundary, a route and a unit. Published figures for steel, aluminium and copper use different boundaries, and each varies several times over by production route. Compare only products with the same declared unit and modules.

What is typical recycled content for stainless steel, aluminium or brass?

Do not quote a typical figure. The bodies read for this sheet give no recycled-content figure for stainless or brass, and for aluminium the IAI asks that the scrap share, its method and its pre- and post-consumer split are disclosed. Ask your supplier for the actual figure.

Do metals have EPDs?

Some industry bodies publish average-product declarations, and some mills publish their own. A bespoke metal piece rarely has one of its own. If you need one, ask early and expect to be told that none exists.

Is recycled aluminium or steel low carbon?

Usually lower than primary, but the amount depends on the route and the data. Ask for the scrap share with its method, and a carbon figure with its boundary. Avoid wording that implies more than the document says.

Can I use one of these figures in a client carbon report?

Only with its source, boundary and year, labelled as an industry average, and with the limits stated. A figure per tonne of crude steel is not a figure for a fabricated piece. See the FF&E carbon sheet for a decision flow.