Methodology

How Slate calculates emissions

This section explains each calculation from how the engine actually works: the formula, a worked example, the published source, and the mistakes each method is built to prevent. Every page links to the official publication so you can check it yourself.

methodology pages

~40

calculators in the engine

publishers

silent defaults

From a record to a number

01
Your record
A fuel, meter reading, journey, herd or tonnage, with a facility and a date.
02
Factor request
What kind of activity, which fuel, where, when. Never which publisher.
03
Resolution
Your publishers are asked in order. Boundaries move on; gaps stop with a reason.
04
Unit conversion
Your quantity is put onto the factor's basis, exactly, or refused.
05
CO₂e
Per-gas factors take your GWP set; pre-calculated CO₂e is used as published.
06
Rows with provenance
Direct, upstream, losses and biogenic rows, each in its scope, each traceable.

Start with factor resolution and CO₂e and gas basis if you want the system as a whole, or jump to the category you report.

Concepts

ConceptsScopes 1, 2 and 3Every figure Slate calculates is filed under a GHG Protocol scope, or deliberately outside all three. Which one decides whether a number can be added to another.ConceptsCO₂e and gas basisPublishers report the same kind of factor in two incompatible ways. Getting this wrong multiplies methane by about 28 a second time, and the result still looks like a reasonable number.ConceptsGWP setsA GWP set turns methane, nitrous oxide and fluorinated gases into CO₂e. Slate holds six, applies one per organisation, and pins it per reporting year.ConceptsReleases and pinningPublishers reissue their factors every year. Slate treats each issue as a fixed release, picks one by the date of each activity, and locks a reporting year to the release it was first calculated with.

The calculation engine

The calculation engineFactor resolutionEvery calculator that needs a factor asks the same function for it. That function walks your organisation's list of publishers in order, and treats "this publisher doesn't cover that" very differently from "this should be here and isn't".The calculation engineMappings and coverageSlate's fuels, vehicles and materials don't use any publisher's vocabulary. A reviewed mapping file connects each one to a publisher's exact row, and a gap is written down with its reason instead of filled with a guess.The calculation engineUnits and conversionYou enter litres; the publisher prices per tonne, or per gigajoule, or per gallon. Slate converts exactly, refuses conversions that don't make physical sense, and never invents a density.The calculation engineUpstream and boundariesA full picture of a fuel or a kilowatt-hour is up to four lines: the direct emission, the upstream emissions of producing it, grid losses, and any biogenic CO₂. Slate writes each as its own row, in its own scope.The calculation engineCalculation jobsCalculating thousands of records takes time, so it runs as a background job. A record that fails is kept and flagged with its reason; it is never dropped from the total.The calculation engineProvenanceEvery calculated row can be traced back to the publisher's file it came from: the release, the publisher's own row reference, the unit exactly as printed, and every publisher that was asked first.

Energy

Energy · Scope 1Stationary combustionFuel burned in boilers, furnaces, ovens and generators. The most common Scope 1 calculation, and the one every other fuel-based calculator is built on.Energy · Scope 1Mobile combustionFuel burned by vehicles and machinery you own or control. EPA publishes the CO₂ against the fuel and the CH₄ and N₂O against the vehicle, so one record is costed in two halves.Energy · Scope 2Scope 2 electricityGrid electricity is reported twice, location-based and market-based, and each can produce up to four rows. Which publisher prices it depends on where the facility is.Energy · Scope 2Heat, steam and coolingEnergy delivered to you by someone else's plant. Each is costed from the fuel or electricity the plant used, so Slate needs to know how efficiently it was made.Energy · Scope 1 and 2On-site renewablesElectricity you generate yourself. Burning biomass for it still emits methane and nitrous oxide; wind and solar emit nothing on site; and either can be credited for the grid electricity it displaced.Scope 1Refrigerant leaksRefrigerant that escapes from cooling equipment. There is no emission factor: the leaked mass is the measurement, and the gas's GWP turns it into CO₂e.Energy · Scope 1Coal, oil and gasMethane released from coal seams and from oil and gas systems, under IPCC Volume 2 Chapter 4. Simple arithmetic; what matters is which published row applies, and which rows can't answer at all.

Value chain

Value chain · Scope 3Scope 3 catalogueSeven kinds of value-chain activity are entered by picking a published activity from a catalogue and supplying the one or two numbers its basis needs. The factor covers the whole activity.

Industrial processes

IPCC Volume 3 · Scope 1Industrial processesEmissions from chemistry, not from burning: limestone giving up its carbon in a kiln, nitric acid plants releasing N₂O, plasma etching fluorinated gases in a chip fab. Seven IPCC chapters, each with one trap worth knowing.

Agriculture and land

IPCC Volume 4 Chapter 10 · Scope 1Livestock and manureMethane from digestion and from stored manure, and nitrous oxide from manure management. The first two are factors per animal; the third depends on how the farm handles manure, so it's a method.IPCC Volume 4 Chapter 11 · Scope 1Soils, lime and ureaNitrogen added to soil comes back as nitrous oxide three ways, and IPCC counts all three. Lime and urea spread on fields give up their carbon as CO₂.IPCC Volume 4 · mostly outside the scopesLand, forests and peatLand is the one place where Slate's figures are often negative. Soil and trees store carbon, and changing how land is used releases it. These are stock changes, not activities, and most are reported outside the three scopes.

Waste

Waste Data module · not an inventoryWaste scenarios (WARM)The Waste Data module compares what happens to the same waste under different pathways. Its figures include avoided emissions, so they answer "what if we changed how we handle this?", never "what did our waste emit?".IPCC Volume 5 Chapter 3 · Scope 1Operated landfillWaste buried in 1994 is still making methane in 2026. So a landfill's emission for one year is a sum over every year of waste before it, decaying at a rate set by what it is and where the site is.IPCC Volume 5 Chapters 4 and 5 · Scope 1Composting and incinerationFor operators of composting sites, digesters and incinerators. Short equations, each with a trap: recovery that's already counted, a weight basis that changes between tables, and CO₂ that's only partly an emission.

Water

Water Data module · GRI 303Water balanceWater accounting in Slate is volumetric: what came in, what was used, what was stored and reused, and whether those add up. It produces no emissions.

Principles

Nothing is defaulted silently

A missing factor, density or GWP stops the calculation with the reason. The record stays visible with its error.

Every figure is traceable

Each row names its release, the publisher's own row, the GWP set and every publisher asked first.

Methods are run, not approximated

Where IPCC publishes a model, such as landfill decay or manure N₂O, Slate runs the model instead of inventing a per-tonne number.

Published inconsistencies are kept

Where a publisher contradicts itself, the printed value is stored and the disagreement is tested, never quietly corrected.

On the roadmap

Net Zero, Life Cycle Assessment and Carbon Market are planned but not built. Their pages say so plainly. For the publishers behind every factor, see Data Sources.