# When a tile or brick unit knows its limestone and dolomite tonnes, should it still use the 85 and 15 percent split?

Canonical: https://senseible.earth/answers/ipcc-ceramics-known-limestone-dolomite-split

No. The Intergovernmental Panel on Climate Change (IPCC) Tier 1 equation uses 85 percent limestone and 15 percent dolomite only when the split is unknown. Its Tier 2 says it is not good practice to use a default allocation. Its reporting section says that where the 85 and 15 default is used, it should be documented.

## The two equations

Tier 1 (Equation 2.14): carbon dioxide (CO2) = tonnes of carbonate x (0.85 x limestone factor + 0.15 x dolomite factor). The blended factor is 0.85 x 0.43971 + 0.15 x 0.47732 = 0.44535 tonnes of CO2 per tonne of carbonate.

Tier 2 (Equation 2.15): CO2 = (tonnes of limestone x its factor) + (tonnes of dolomite x its factor). Under it the guide says: "It is not good practice to use a default for the allocation between these two primary carbonates."

## What to keep

- Purchase and issue slips that name limestone and dolomite separately.
- Tonnes as pure carbonate. If you only know the weight of carbonate rock, the guide says a default purity of 95 percent can be assumed.
- A note wherever the 85 and 15 default is used: the guide says this should be documented.

## How big the difference is

The default sits about 1.3 percent above an all-limestone answer and about 6.7 percent below an all-dolomite answer. The more dolomite you really use, the more the default understates.

## Does a national tier apply to one unit

The guide writes Tiers 1 and 2 for national data. Applying the same rule to one unit's records is my reading: the equations are the same and the data are yours.

## A unit that buys both

- Bought: 18.0 tonnes of limestone and 12.0 tonnes of dolomite, 30.0 tonnes in all
- Default split: 30.0 x 0.44535 = 13.361 tonnes of CO2
- Known split: 18.0 x 0.43971 = 7.915, and 12.0 x 0.47732 = 5.728, total 13.643 tonnes
- Difference: 0.282 tonnes, 2.1% of the default. To two significant figures the two read 13 and 14.

Tonnes are example numbers, taken as pure carbonate with full calcination.

## What Senseible does here

Senseible reads fuel invoices and electricity bills into monthly records, so the fuel and power lines of a furnace or kiln are on file. In the self-serve product it does not read limestone or dolomite purchases as process emissions, so the split comes from your own purchase slips.

- [Process CO2 for clay products without an assay](https://senseible.earth/answers/process-co2-from-clay-bricks-tiles-without-lab-assay)
- [Fraction calcined when not measured](https://senseible.earth/answers/ipcc-fraction-calcined-unknown-ceramics-glass)
- [Which limestone uses release CO2](https://senseible.earth/answers/which-limestone-uses-release-carbon-dioxide)
- [Sanitaryware carbon footprint per piece](https://senseible.earth/answers/sanitaryware-carbon-footprint-per-piece)

Sources: [IPCC, 2006 Guidelines, Volume 3, Chapter 2: Mineral Industry Emissions](https://www.ipcc-nggip.iges.or.jp/public/2006gl/pdf/3_Volume3/V3_2_Ch2_Mineral_Industry.pdf)

Last reviewed 2026-11-06. Quotes and figures are from the 2006 IPCC Guidelines, Volume 3, Chapter 2. The 2019 Refinement was not checked for this page; check it if a buyer names it.