> ## 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.

# How emissions are calculated

> The calculation chain behind every number in Salvidia, from raw data to tonnes of CO₂e.

Every figure in Salvidia comes from the same simple equation, applied thousands of times across your data:

> **Emissions = activity data × emission factor**

This page walks through what each side of that equation means, and how individual calculations roll up into your footprint.

## Activity data: the "how much"

Activity data quantifies something your organisation did. It comes in two forms:

<Columns>
  <Column>
    <Card title="Physical quantities">
      Kilowatt-hours of electricity, litres of diesel, kilometres flown, tonnes of waste. This is the more accurate form — it measures the activity directly.
    </Card>
  </Column>

  <Column>
    <Card title="Spend">
      Dollars spent on a category of goods or services. Used when physical quantities aren't available — which, for most of a supply chain, is the practical reality.
    </Card>
  </Column>
</Columns>

## Emission factors: the "how dirty"

An emission factor converts a unit of activity into greenhouse gas emissions — kilograms of CO₂e per kWh, per litre, per dollar spent in an industry. Factors come from published, referenced sources and vary by geography (the same kWh has a very different footprint on different electricity grids) and by category. How Salvidia selects them is covered in [Emission factors](/methodology/emission-factors-overview).

## A worked example

Say your ledger and bills for the year contain:

| Input             | Activity data | Factor type                        | Result  |
| ----------------- | ------------- | ---------------------------------- | ------- |
| Electricity       | 42,000 kWh    | Grid factor (kg CO₂e/kWh)          | Scope 2 |
| Fleet diesel      | 6,500 L       | Fuel factor (kg CO₂e/L)            | Scope 1 |
| Flights           | 38,000 km     | Aviation factor (kg CO₂e/km)       | Scope 3 |
| Contract services | \$180,000     | Industry spend factor (kg CO₂e/\$) | Scope 3 |

Each line is calculated independently: quantity × factor = kg CO₂e. Each result is tagged with its **scope** and **category**, and the totals you see on the dashboard are simply the sum of every one of these line-level calculations. There's no adjustment layer between the data and the total.

## Why this matters for audit

Because the chain is *data → factor → line result → total*, every number in a Salvidia report can be decomposed back to its inputs:

1. **The total** breaks into scopes and categories
2. **A category** breaks into the individual entries inside it
3. **An entry** shows its activity data and the factor applied

That traceability is what "audit-ready" actually means: not a certificate, but the ability to answer "where did this number come from?" at every level, with sources.

## CO₂e and global warming potentials

Different greenhouse gases trap different amounts of heat. Methane, refrigerants, and nitrous oxide are far more potent than CO₂ per kilogram. Emission factors already account for this by converting everything to **CO₂ equivalent (CO₂e)** using published global warming potentials — which is why one unit can describe your entire footprint.

## The accuracy hierarchy

Not all inputs are equal, and the methodology is honest about that:

1. **Measured physical data** (metered kWh, fuel receipts) — most accurate
2. **Calculated physical data** (distances from travel records) — very good
3. **Spend-based estimates** (industry-average factors on your ledger) — broad coverage, lower precision

The standard practice: use spend for coverage, then upgrade your **largest categories** to physical data over time. Each upgrade tightens the whole footprint where it matters most. See [Activity-based vs spend-based](/guides/activity-based-vs-spend-based) for the full trade-off.