How many digits can a ceramic or glass unit's process carbon dioxide figure carry under the Intergovernmental Panel on Climate Change tables?

The Intergovernmental Panel on Climate Change (IPCC) note under its carbonate table says final results using its factors should be rounded to no more than two significant figures. So 1,481.5 tonnes of carbon dioxide (CO2) from soda ash and limestone is reported as 1,500, with the full figure kept in your working.

What the note says

Under Table 2.1 of the IPCC 2006 Guidelines, the note marked with one asterisk reads: "Final results (i.e., emission estimates) using these data should be rounded to no more than two significant figures." The table itself prints factors to five digits, such as 0.43971 tonnes of CO2 for each tonne of calcite and 0.41492 for soda ash.

This note covers the IPCC process line. Two significant figures means 1,481.5 becomes 1,500, 892.08 becomes 890 and 0.0476 becomes 0.048.

Keep full digits until the last step

The note speaks of final results. Rounding each carbonate first and then adding can shift the total, so round once, at the end. That is my reading of the word final.

1. Weigh each carbonate in tonnes, as the weighbridge or issue slip gives it.
2. Multiply by the table factor with all its digits, and by the fraction calcined if you use one.
3. Add the carbonates together.
4. Round only the final total, to two significant figures.

Why two digits is fair

The guide puts the weighing of carbonates at about 1 to 3 percent uncertainty, their chemical analysis at 1 to 3 percent, and a purity assumption at plus or minus 1 to 5 percent where only rock weights are known. A figure with six digits would claim a precision those inputs do not have. Tying the note to those percentages is my reading; the note itself gives no reason.

Where the note stops

• It sits under the IPCC carbonate table. It sets no rule for fuel invoices, electricity bills or a buyer's form.
• It is written for a result built from Table 2.1 factors in an IPCC-style process line. The wider report follows the rounding page linked below, which shows MSME scope totals in tonnes with one decimal, such as 59.4 t. How the two fit is my reading: round the process line as the IPCC note says, and present scope totals as that page advises.
• If a buyer's template has room for more digits, give what they ask for and keep your own record at full precision. The note says what a result should be rounded to, not what a spreadsheet may store. This too is my reading.

A glass month: soda ash and limestone

• Soda ash: 2,150.0 tonnes x 0.41492 = 892.078 tonnes of CO2
• Limestone: 1,340.5 tonnes x 0.43971 = 589.431 tonnes of CO2
• Total: 892.078 + 589.431 = 1,481.509 tonnes
• Reported to two significant figures: 1,500 tonnes

Tonnes are example quantities, taken as pure carbonate with all of it calcined. 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 sit on record. Carbonate tonnes come from your own weighbridge and issue records, so keep the full-digit working beside the report.

• IPCC glass factors and cullet ratios
• Process CO2 for clay products without an assay
• Firozabad glass batch carbonates
• Rounding numbers in a carbon footprint report
• Emissions calculators

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.