# Why does the buy to fly ratio matter so much for an aerospace part's carbon footprint?

Canonical: https://senseible.earth/answers/aerospace-part-buy-to-fly-ratio-carbon

Because you pay for the carbon in all the metal you buy, not just what flies. Machined titanium and aluminium parts can start from billets many times their finished weight, so material production dominates. Count the whole bought weight at the supplier's figure, and report chips sold for recycling separately.

## The arithmetic

- Bought weight = finished weight x buy to fly ratio.
- Material footprint = bought weight x supplier figure per kg.
- Add machining electricity and coolant handling from your plant.

## Chips and scrap

Chips sold to recyclers are not subtracted from your figure. Report them as waste or sold scrap, with tonnes.

## Where to cut

Near net shape forgings, castings or additive preforms lower the ratio, and recycled content titanium or aluminium lowers the per kg figure. Show both changes with evidence.

## Worked example: a 2 kg titanium bracket

- Buy to fly 8:1, so 16 kg of titanium bought
- 16 kg x supplier figure per kg = material footprint
- Plus machining kWh x grid factor

Ratio and figures are illustrative; use your own routing and supplier data.

## What Senseible does here

Senseible reads metal, electricity and fuel invoices into a dated, fingerprinted record, so bought weight and energy behind a part figure trace back to the documents.

- [CNC machined part footprint](https://senseible.earth/answers/cnc-machined-part-carbon-footprint)
- [Selling production scrap](https://senseible.earth/answers/selling-production-scrap-scope-3-category-5)
- [Queretaro aerospace supplier data](https://senseible.earth/answers/queretaro-aerospace-supplier-carbon-data)

Sources: [ISO 14067:2018, Carbon footprint of products (iso.org)](https://www.iso.org), [GHG Protocol Product Standard](https://ghgprotocol.org/standards)

Last reviewed 2026-10-21.