How should a glass unit that counts bottles or square metres turn its output into tonnes for the Intergovernmental Panel on Climate Change method?

The Intergovernmental Panel on Climate Change (IPCC) says glass data given in bottles or square metres should be converted into tonnes, and that the conversion may add uncertainty on top of about plus or minus 5 percent for mass data. The equation uses glass melted, so add rejects and breakage back.

What the guide says

• "Data for glass often is provided in different units (e.g., tonnes of glass, number of bottles, square meters of glass, etc.) and these should be converted into tonnes."
• Documentation should include any calculation used "to convert different types of glass into the same units (e.g., convert bottles into kilogram)."
• Glass production data are typically measured fairly accurately, plus or minus 5 percent, for Tier 1 and Tier 2. But "If activity data have to be converted to mass, this may result in additional uncertainty."

Melted, not sold

The equation takes mass of melted glass. Bottles packed are fewer than bottles melted, because rejects and breakage return to the furnace as cullet. Convert good pieces to tonnes, then divide by the pack-to-melt yield your records show. The guide does not define the yield; measuring melt as glass drawn from the furnace is my reading. For emissions per tonne of product the divisor stays good glass packed, as on the container furnace page; the melt tonnes here are for the carbonate line only.

Square metres

For flat glass or mirror, area is not mass. Multiply area by thickness and by the density of your glass from the supplier's data sheet. The guide gives no density.

Then pick the factor

Take the factor for your glass type and cullet ratio from the IPCC glass factors page linked below. The example uses its flint container figures.

Flint container glass, one month

• Good bottles: 1,200,000 x 0.300 kilograms = 360 tonnes
• Melt at a 92% pack-to-melt yield: 360 / 0.92 = 391.3 tonnes
• Factor: 0.21 tonnes of carbon dioxide (CO2) per tonne of glass x (1 minus 0.45) = 0.1155
• Batch CO2: 391.3 x 0.1155 = 45.2 tonnes, reported as 45

Bottle weight and yield are example numbers. This is the carbonate part only; furnace fuel and electricity are separate lines.

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 count bottles or square metres, so the conversion to tonnes stays in your production records.

• IPCC glass factors and cullet ratios
• Glass bottle carbon footprint per bottle
• Glass container furnace emissions per tonne
• Cullet records: in-house or bought in

Sources: IPCC, 2006 Guidelines, Volume 3, Chapter 2: Mineral Industry Emissions

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.