When you begin building a carbon inventory, the first few weeks give you a deceptive sense of ease. Scope 1 and 2 — the fuel you burn directly and the electricity you purchase — flow readily from invoices, metering devices, and energy company reports. After a month of disciplined work, the team looks at the spreadsheet and says, "we're done."
But you've only completed 20-30% of your inventory. The remainder — Scope 3 — comes from your supply chain, the services you use, your employees' travel, and the products you buy. You can't see it because you don't measure it. You don't measure it because the source data belongs to someone else.
15 categories, one accountability question
The GHG Protocol divides Scope 3 into fifteen categories — seven upstream and eight downstream. This structure provides a useful skeleton for thinking, but not every category is material for every company. If you're a software company, purchased goods and services may account for half your inventory; if you're a manufacturer, use of sold products may carry more weight.
Our recommendation: don't try to tackle all 15 categories like homework to be handed in overnight. Start with a materiality assessment, then go deeper on the significant ones.
A Scope 3 inventory that waits to be perfect never gets started. What matters is not the accuracy of the measurement, but the existence of the measurement and its year-on-year improvement.— GHG Protocol Scope 3 Standard, §4.2
Data quality: three tiers
For every category there are at least three tiers of data collection: primary data (actual emissions obtained directly from your supplier), average data (blended using sector emission factors), and spend-based data (purchase value × emission intensity factor).
Primary data is the most accurate but the hardest to collect. Requesting carbon inventories from suppliers requires a relationship, a template, and often an incentive. Spend-based data is the easiest but the coarsest — a 100,000-TL equipment purchase generates the same emissions figure regardless of who manufactured it. Most companies begin the journey with spend-based data and upgrade material categories to primary data over time.
- Primary data: supplier-specific emission factor or actual consumption.
- Secondary data: sector average, country-average emission factor.
- Spend-based data: TL × kg CO₂e / TL (Exiobase, Defra, USEEIO).
A starter kit for Turkish companies
If you operate in Turkey and have not yet begun your Scope 3 inventory, here is the three-week start our team recommends:
Week 1 — Screening
Review all 15 categories, quickly estimate their order of magnitude (spend-based, rough calculation), and identify which categories cross the 1% threshold. This is called screening.
Week 2 — Prioritisation
Select the material categories (usually 3-5). For each one, define your data source, the responsible team, and your target accuracy level.
Week 3 — First calculation
Run the first calculation using secondary data and emission factors. Prepare a year-on-year improvement plan. This becomes your year-one inventory — imperfect but real, and auditable.
Next step: automation with Carbonlogy
The Carbonlogy platform automates Scope 3 calculation starting from your invoices. Document scanning, emission factor matching, and data quality scoring — all within the system. It can compress your three-week screening effort into a single afternoon.
Even so — understand the framework first. If automation speeds up something you don't understand, it only speeds up the mistake.
— Defne, May 2026