Convert Price per tCO₂ to Price per tC
| price per tCO₂ | price per tC |
|---|---|
| 0.5 | 1.833 |
| 1 | 3.667 |
| 1.5 | 5.5 |
| 2 | 7.333 |
| 3 | 11 |
| 5 | 18.33 |
| 10 | 36.67 |
| 20 | 73.33 |
| 50 | 183.3 |
| 100 | 366.7 |
Each row uses the same factor as the converter above: 1 price per tCO₂ = 3.667 price per tC.
A price of $100 per tonne of CO₂ is $366.67 per tonne of carbon. The two are not alternative ways of saying the same thing — they differ by a factor of 3.67, and a figure quoted on the wrong one is not slightly off, it is nearly four times wrong. This is the oldest ambiguity in carbon pricing, and it is still live in the literature.
To convert a price per tonne of CO₂ into a price per tonne of carbon, multiply by 3.667. So $50/tCO₂ is $183.33/tC. To go the other way, divide by 3.667 — $100/tC is $27.27/tCO₂. The ratio is the mass of CO₂ produced by burning a tonne of carbon.
Price per tC = price per tCO₂ × 44/12 (= 3.66667). Reverse: price per tCO₂ = price per tC × 12/44. The ratio is stoichiometric: one carbon atom (relative mass 12) burns to one CO₂ molecule (relative mass 44), so a tonne of carbon becomes 3.667 tonnes of CO₂.
| Price per tCO₂ | × 3.667 | Price per tC |
|---|---|---|
| $25 | × 3.667 | $91.67 |
| $50 | × 3.667 | $183.33 |
| $100 | × 3.667 | $366.67 |
| $150 | × 3.667 | $550.00 |
How to convert between the two bases
Multiply by 3.667 to go from a carbon dioxide basis to a carbon basis, and divide by it to come back. The direction that trips people up is the second one: a price quoted per tonne of carbon always looks larger, so converting it to the CO₂ basis makes the number smaller.
The sanity check is to ask which unit is doing more work. A tonne of carbon represents 3.667 tonnes of eventual CO₂, so it is the bigger unit in emissions terms — and the price attached to a bigger unit is higher. The number follows the size of the unit underneath it, the same rule that governs every intensity conversion on this site.
Which basis is which, and where each turns up
| Basis | Written as | Where you meet it |
|---|---|---|
| Carbon dioxide | $/tCO₂ or $/tCO₂e | Emissions trading, carbon taxes, offset markets, corporate disclosure — effectively all current practice |
| Carbon | $/tC | Older climate economics, some academic literature, a few legacy tax instruments and integrated assessment models |
Almost everything transacted today is on the carbon dioxide basis. The EU ETS, the UK ETS and national carbon taxes all settle per tonne of CO₂ or CO₂-equivalent. The carbon basis survives mainly in economics, which is precisely where the highest-profile numbers come from — so a social cost of carbon lifted from a paper and dropped into a compliance model is the classic way to overstate a price by 3.67 times.
The error is easy to make and hard to spot, because both figures look plausible. A shadow price of $300 sounds ambitious against an ETS settling near $80 — until you notice the $300 is per tonne of carbon, which is $82 per tonne of CO₂ and therefore almost exactly the market. Whenever two carbon prices seem implausibly far apart, check whether one of them is on the carbon basis before concluding anything. The same applies in reverse: a suspiciously modest academic figure may be a CO₂-basis number being read as carbon.
Why 44/12 and not 3.664
Two versions of this ratio circulate, and they differ by 0.07 per cent.
| Ratio | Value | Basis | Used for |
|---|---|---|---|
| 44 / 12 | 3.66667 | Stoichiometric, IPCC and GHG Protocol reporting convention | This page, and carbon to CO₂ |
| 44.009 / 12.011 | 3.66406 | Molar masses to three decimals | GtC to Gt CO₂, the carbon-budget convention |
This page uses 44/12, because a carbon price is a compliance and markets quantity and belongs with the reporting convention. The difference could never change a pricing decision — but a page disagreeing with the mass conversion it is derived from would be a genuine inconsistency, so the two match by design.
What this does not do
This converts a price basis. It does not tell you what to pay, what you owe, or whether a price is right. For a liability figure use the carbon tax liability calculator or the EU ETS allowance calculator; for setting an internal price, the internal carbon price calculator and its methodology; for what abatement costs, the marginal abatement cost calculator.
For the underlying mass relationship rather than the price, carbon to CO₂ and tC to tCO₂e. For carbon prices at product scale, carbon price per tonne to per kg. For the carbon-budget basis, GtC to Gt CO₂.
Frequently Asked Questions
Multiply by 3.667. So $100 per tonne of CO₂ is $366.67 per tonne of carbon. To reverse it, divide by 3.667 — $100 per tonne of carbon is $27.27 per tonne of CO₂.
Because a tonne of carbon becomes 3.667 tonnes of CO₂ when burned, so it is the bigger unit in emissions terms and carries a proportionally bigger price. The number always follows the size of the unit underneath it.
Carbon dioxide, effectively without exception. Emissions trading schemes, carbon taxes, offset markets and corporate disclosure all settle per tonne of CO₂ or CO₂-equivalent. The carbon basis survives mainly in older climate economics and integrated assessment modelling.
Read the unit carefully — tCO₂ or tCO₂e means the carbon dioxide basis, tC means carbon. If the source does not say, the context usually does: anything transacted or regulated is almost certainly CO₂, while an economics paper may well be carbon. If two prices seem implausibly far apart, a basis mismatch is the first thing to check.
Both are in use and they differ by 0.07 per cent. 44/12 = 3.66667 is the stoichiometric ratio used by the IPCC and GHG Protocol for reporting, and it is what this page uses. 44.009/12.011 = 3.664 uses molar masses to three decimals and is the convention in carbon-budget work. The difference cannot change a pricing decision; consistency with the reporting convention can.
Yes for the arithmetic, but treat it carefully. The 3.667 ratio is the mass relationship between carbon and carbon dioxide specifically. A CO₂-equivalent price covers other gases converted by their global warming potential, so a “per tonne of carbon” restatement of a CO₂e price is really saying “per tonne of carbon’s worth of CO₂-equivalent”, which is a defensible shorthand but not a physical statement about those other gases.
No — it converts a price between two bases. What you actually owe depends on your emissions, the scheme you fall under, free allocation, and any exemptions. The carbon tax liability and ETS allowance calculators handle that; this page only makes sure the price you feed them is on the basis you think it is.
Because climate economics developed before carbon markets did, and it worked in tonnes of carbon — the quantity extracted and burned. Markets, which had to price something measurable at the point of emission, settled on carbon dioxide. Both conventions persisted, and the literature still crosses between them, so the factor of 3.67 keeps resurfacing wherever academic and market figures are compared.