Convert tC to tCO2e
A tonne of carbon and a tonne of carbon dioxide are not the same quantity — and confusing them is one of the most common and costly mistakes in greenhouse-gas accounting. To express a mass of elemental carbon (tC) as the carbon dioxide it becomes when fully oxidised, you multiply by 44/12 ≈ 3.667. This converter does that transformation in both directions, and the sections below explain exactly why the factor is what it is and where the tC↔tCO2e boundary trips up forestry, carbon-credit and inventory reporting.
To convert tonnes of carbon (tC) to tonnes of CO2-equivalent (tCO2e), multiply by 44/12 ≈ 3.667. So 1 tC = 3.667 tCO2e. To reverse it, divide by 3.667 (× 12/44). The factor is the molecular-mass ratio of CO2 (44) to carbon (12).
A reforestation project stores 500 tonnes of carbon (500 tC) in new above-ground biomass. Expressed as carbon dioxide removed from the atmosphere:
| Step | Calculation | Result |
|---|---|---|
| Carbon stored | — | 500 tC |
| Apply the 44/12 ratio | 500 × 3.667 | 1,833 tCO2e |
The same 500 tC reported as if it were already 500 tCO2e would understate the climate quantity by a factor of 3.667 — a 267% error.
How to convert tonnes of carbon (tC) to tonnes of CO2e
Carbon is one element; carbon dioxide is one carbon atom bonded to two oxygen atoms. When carbon is fully oxidised — burned, respired, or otherwise converted to CO2 — each unit of carbon mass gains the mass of two oxygen atoms. Because relative atomic masses are carbon ≈ 12 and oxygen ≈ 16, one “molecule unit” of CO2 weighs 12 + (2 × 16) = 44. The mass therefore scales by 44 ÷ 12.
The formula
tCO2e = tC × 44 ÷ 12 = tC × 3.6667
The result is expressed as CO2-equivalent (tCO2e) rather than plain tCO2 purely as an accounting convention — see the tCO2 vs tCO2e note below. No global warming potential is applied in this conversion; it is pure stoichiometry. The factor is identical on any mass basis — for the same conversion expressed per kilogram, use the carbon to CO2 converter.
Converting back: tonnes of CO2e to tonnes of carbon
To recover the mass of carbon contained in a quantity of CO2, invert the factor — divide by 3.667, or equivalently multiply by 12 ÷ 44 ≈ 0.2727. Use the swap control on the converter above to switch direction.
tC = tCO2e × 12 ÷ 44 = tCO2e × 0.27273
tC to tCO2e conversion table
Common values, rounded to four significant figures. The forward column applies × 3.667; the reverse table applies × 0.2727.
| Tonnes carbon (tC) | × 44/12 | Tonnes CO2e (tCO2e) |
|---|---|---|
| 0.5 | × 3.667 | 1.833 |
| 1 | × 3.667 | 3.667 |
| 5 | × 3.667 | 18.33 |
| 10 | × 3.667 | 36.67 |
| 25 | × 3.667 | 91.67 |
| 50 | × 3.667 | 183.3 |
| 100 | × 3.667 | 366.7 |
| 500 | × 3.667 | 1,833 |
| 1,000 | × 3.667 | 3,667 |
| Tonnes CO2e (tCO2e) | × 12/44 | Tonnes carbon (tC) |
|---|---|---|
| 1 | × 0.2727 | 0.2727 |
| 5 | × 0.2727 | 1.364 |
| 10 | × 0.2727 | 2.727 |
| 100 | × 0.2727 | 27.27 |
| 1,000 | × 0.2727 | 272.7 |
Both units here are tonnes; the 44/12 ratio changes the substance basis, not the mass prefix. To move between mass prefixes on a single substance — for example kilograms to tonnes of CO2e — use the kg CO2e to tonnes converter instead.
Why the tC vs tCO2e distinction matters in carbon accounting
The arithmetic is trivial, but the stakes are not. The tC↔tCO2e boundary sits at the heart of forestry and land-sector reporting, carbon-credit issuance, and national greenhouse-gas inventories — precisely the places where a silent factor-of-3.667 error changes the headline number by 267%.
Scientific and forestry literature frequently reports carbon stock in tonnes of carbon (tC, or MgC, or tC/ha). Carbon markets and corporate inventories report in tonnes of CO2e. Copy a “tC” figure straight into a “tCO2e” field without applying 44/12 and you understate the CO2 quantity by 3.667×; do the reverse and you over-issue credits or over-claim removals by the same factor. Always confirm which unit a source is using before combining figures.
Is tCO2 the same as tCO2e?
For this conversion, yes — 1 tCO2 = 1 tCO2e exactly. The “e” (equivalent) signals that a quantity has been expressed on a CO2 basis using each gas’s global warming potential. Carbon dioxide has a GWP of 1 by definition, so its mass and its CO2-equivalent mass are identical. The “e” here is an accounting convention, not a second multiplication — there is no hidden GWP factor inside the 44/12 ratio.
3.667 vs 3.664 — stoichiometric vs molar-mass basis
You will see two closely related factors. The stoichiometric ratio 44/12 = 3.6667 uses whole-number atomic masses and is the convention in the GHG Protocol, IPCC AFOLU guidance, and voluntary carbon markets — use it for inventory and credit accounting. The molar-mass ratio 44.009/12.011 = 3.6641 uses precise standard atomic weights and appears in carbon-budget and atmospheric science — it is the basis used by the GtC to Gt CO2 converter. The two differ by about 0.07%; this converter uses 44/12, the accounting standard.
The carbon-fraction trap: biomass is not carbon
Dry biomass is only roughly 47–50% carbon by mass. Converting a tonne of biomass to CO2 is a two-step chain: first apply the carbon fraction (biomass × ~0.47 = carbon), then apply 44/12 to that carbon. Applying 44/12 directly to biomass mass skips the carbon fraction and roughly doubles the answer. This converter handles only the second step — carbon to CO2. To estimate carbon stock from biomass, area, or growth data, use the calculators linked below.
Where tC and tCO2e are used: standards and reporting conventions
Knowing which unit a framework expects is half the battle. The 44/12 conversion is the bridge between the two conventions across the emissions landscape:
- IPCC AFOLU guidance — carbon-stock changes in biomass, dead organic matter and soils are tracked in tonnes of carbon, then converted to CO2 with 44/12 for reporting.
- Voluntary carbon markets — Verra VCS, Gold Standard and similar registries issue credits denominated in tCO2e; underlying forestry measurements often arrive in tC.
- National greenhouse-gas inventories — land-use and forestry (LULUCF) sectors convert measured carbon flux to CO2 for the reported totals.
- Carbon budgets and atmospheric science — cumulative-emissions budgets are frequently stated in GtC (gigatonnes of carbon), converted to Gt CO2 with the molar-mass ratio (see above).
- Fuel and combustion accounting — a fuel’s carbon content maps to combustion CO2 via the same 44/12 ratio.
Need to estimate the carbon stock behind a tC figure — from tree biomass, land-use change, or an engineered removal — rather than just convert a known value?
Frequently Asked Questions
Multiply the mass of carbon by 44/12 ≈ 3.667. For example, 10 tC × 3.667 = 36.67 tCO2e. The factor is the molecular-mass ratio of carbon dioxide (44) to elemental carbon (12): oxidising carbon to CO2 adds the mass of two oxygen atoms.
Carbon has a relative atomic mass of about 12 and oxygen about 16. A CO2 molecule is one carbon plus two oxygens: 12 + 32 = 44. So each unit mass of carbon becomes 44/12 = 3.667 units of CO2 mass when fully oxidised.
For carbon dioxide, yes: 1 tCO2 = 1 tCO2e. The “e” means CO2-equivalent — a mass converted to a CO2 basis using each gas’s global warming potential. Because CO2 has a GWP of 1 by definition, its equivalent mass equals its actual mass. There is no extra GWP factor in the 44/12 conversion.
3.6667 uses whole-number atomic masses (44/12) and is the convention for GHG inventories, IPCC AFOLU and carbon-credit accounting. 3.6641 uses precise standard atomic weights (44.009/12.011) and is used in carbon-budget and atmospheric science, such as converting GtC to Gt CO2. They differ by about 0.07%; this converter uses the accounting standard, 44/12.
Divide by 3.667, or multiply by 12/44 ≈ 0.2727. For example, 100 tCO2e × 0.2727 = 27.27 tC. Use the swap control on the converter to switch direction.
No. The tC-to-tCO2e conversion is pure stoichiometry and is identical under AR4, AR5 and AR6, and under any time horizon. GWP values only matter when converting other greenhouse gases (methane, N2O, refrigerants) to CO2e. Carbon dioxide’s GWP is fixed at 1.
No. Dry biomass is only about 47–50% carbon, so you must first multiply biomass mass by the carbon fraction (≈ 0.47) to get carbon, then apply 44/12. Applying 44/12 directly to biomass skips a step and overstates the CO2 by roughly two-fold. This converter handles carbon to CO2 only.