> ## Documentation Index
> Fetch the complete documentation index at: https://docs.salvidia.com/llms.txt
> Use this file to discover all available pages before exploring further.

# Emission factors

> Where Salvidia's emission factors come from, how they're chosen, and why the same activity can have different factors.

An **emission factor** is the conversion rate between an activity and its emissions: kilograms of CO₂e per kilowatt-hour, per litre of fuel, per passenger-kilometre, or per dollar spent in an industry. They're the second half of every calculation Salvidia performs, and the credibility of your footprint rests on where they come from.

## Sourcing principles

Salvidia applies factors from **published, referenced sources** — not proprietary numbers that can't be checked. In practice that means:

* **Government-published factors** for energy, fuels, and transport in the relevant country. For Australian assessments this includes the factors published by the Australian Government for national greenhouse accounting, which cover grid electricity by state, fuels, and waste.
* **Recognised international factor sets** where an activity isn't covered by a local source, or where the activity happens outside Australia.
* **Industry-level spend factors** for converting expenditure into estimated emissions, matched to the category of goods or services purchased.

Every factor applied in your assessment is attributable to its source, which is what allows a reviewer to check any line of the calculation.

## Why the same activity can have different factors

Three legitimate reasons, worth understanding because they explain most "why doesn't this match tool X?" questions:

1. **Geography.** A kWh of grid electricity in Victoria has a different factor than one in Tasmania, because the generation mix is different. Factors are matched to where the activity happened.
2. **Vintage.** Factor sets are updated as grids decarbonise and methods improve. Two assessments run against different factor years can differ with identical data — which is also why your electricity emissions can fall even when usage doesn't.
3. **Method.** A flight calculated per-kilometre and a flight estimated from ticket spend will produce different results. Neither is wrong; the physical method is simply more precise.

<Note>
  When comparing your results with output from another tool, the first things to check are the factor source, the factor year, and whether the same categories used spend or activity data. In almost every case, that's where the difference lives.
</Note>

## Spend-based factors and their limits

Spend factors represent the **average emissions intensity of an industry per dollar**. They're what makes full supply-chain coverage possible without surveying every supplier, and they're a recognised part of GHG Protocol Scope 3 practice.

Their limitation is that they can't see supplier-level differences: a dollar spent with a renewable-powered printer and a dollar spent with a coal-powered one carry the same estimate. That's why the methodology treats spend factors as the starting point, upgraded to physical data or supplier-specific information in your material categories over time.

## How factors are applied in your assessment

When data enters Salvidia, each entry is matched to a factor based on its **category, unit, location, and period**. You don't select factors by hand — the matching is systematic, which keeps assessments consistent and comparable year over year.

***

## Where to go next

* [How emissions are calculated](/methodology/how-emissions-are-calculated)
* [Standards and frameworks](/methodology/standards-and-frameworks)