- Activity-based uses what physically happened: kWh, litres, kilometres, tonnes.
- Spend-based uses how much money changed hands, with per-dollar factors by industry.
The difference in one line
Activity data measures the thing. Spend data prices it and infers the thing.
Salvidia converts both into CO₂e using published emission factors. Activity data is closer to reality because it does not move when your prices do.
Why activity data is preferred
Physical quantities are directly linked to emissions, which gives you three advantages:- Stability. Your result does not shift because a supplier raised prices or the exchange rate moved.
- Comparability. You can compare sites and years honestly, because the unit means the same thing every time.
- Actionability. Reduction projects are designed in litres and kilowatt-hours, not dollars. “Use less fuel” is a plan. “Spend less on fuel” might just mean prices fell.
Why spend data still matters
Nobody collects meter readings from their accountant, their software vendors, or the agency that made their brochures. Spend-based factors exist so those categories are not simply missing. They work by applying an industry-average emissions intensity per dollar. That makes them ideal for:- Professional services, marketing, software, office supplies
- Long-tail vendors where collecting activity data is unrealistic
- A first-pass footprint, before you know which categories matter
Deciding which to use
Use activity-based when the data is metered or measurable, the category is material, or you are planning reductions there. Use spend-based when activity data is genuinely hard to get, the category is a long tail of small purchases, or you are still screening for a baseline.You do not choose one for your whole footprint. Strong inventories use activity data for the big categories and spend for the long tail, then shift the balance each year.
Worked examples
Electricity. Use kWh from meter readings or bills. Avoid spend-based factors here: kWh is usually easy to obtain and electricity is often material. Record it as kWh, not dollars. Business travel. For flights, distance and class per flight beats total spend by a wide margin. For hotels, nights by city and type if you have them, spend if you only have the expense total. Record flights and hotel nights as quantities wherever the booking data supports it. Purchased services. Marketing, legal, IT. There is rarely a practical activity metric, so spend-based is appropriate. Improve it over time through better categorisation and supplier-specific data where a supplier publishes real figures. Waste. Tonnes per stream from your waste contractor, falling back to spend on waste services. Record it by weight where possible.How Salvidia handles both
Energy, travel, and waste are activity-first: they expect physical quantities. Purchased goods and services is flexible and accepts either method. Behind the scenes, Salvidia detects whether a row is activity-based or spend-based, applies the matching factor type, and stores both the input and the method used. That last part matters: you can always see which approach produced any given number, which is what lets you upgrade categories deliberately rather than guessing what is already good.The upgrade path
The practical rule for every footprint: let spend give you coverage, then upgrade your largest categories to activity data.1
Prioritise by impact
Use activity data first for categories you expect to be large: energy, travel, materials. Precision in a category worth 0.3% of your total is wasted effort.
2
Use spend to fill the gaps
Where activity data is impractical, spend-based factors keep the category present rather than silently missing.
3
Document your choices
Note where you used each method and why. This is what makes year-on-year comparisons meaningful instead of confusing.
4
Upgrade one to three categories a year
Pick a small number and improve them properly, rather than trying to perfect everything at once.