Introduction to greenhouse gas mass and CO₂ equivalent
Carbon dioxide is the best-known greenhouse gas, but an emissions inventory often includes methane, nitrous oxide and fluorinated gases as well. Those gases do not produce equal warming kilogram for kilogram. Carbon dioxide equivalent, written CO₂e, places them on a common scale so that their effects can be compared and added. The conversion multiplies the mass of each gas by its 100-year global warming potential, or GWP100, and then totals the products.
This greenhouse gas calculator accepts direct masses of CO₂, CH₄, N₂O and one optional fluorinated gas. It supports IPCC AR4, AR5 and AR6 factors because reporting programs do not all use the same assessment report. It also distinguishes fossil methane from non-fossil methane where the chosen report provides separate factors. The result includes a total in kilograms and metric tonnes of CO₂e, a gas-by-gas table and a contribution chart that reveals which source dominates the footprint.
Every mass should cover the same physical and reporting boundary. For example, all entries might describe one facility during one calendar year, one manufacturing batch or one journey. Combining annual carbon dioxide with weekly methane would produce valid arithmetic but an invalid inventory. The calculator cannot detect that kind of boundary mismatch, so confirm the period before interpreting the total.
How to use this greenhouse gas CO₂e calculation
Begin by selecting the assessment report required by your inventory framework. AR6 reflects the most recent science offered here, while AR4 and AR5 remain useful when a regulator, customer or historical baseline mandates them. Keeping the factor set consistent is essential when comparing years. A change in GWP values can move the reported total even when the underlying gas masses have not changed.
Next, choose one mass unit for the calculation. The unit applies to every gas field, including the fluorinated gas mass. Enter zero for a gas that is not present. If methane is included, identify whether it comes from a fossil source such as oil, natural gas or coal operations, or a non-fossil source such as livestock, landfill, wastewater or biogenic digestion. Finally, select an F-gas only if its corresponding mass is known. The calculator prevents an unidentified F-gas mass from being included because these gases have very different multipliers.
After selecting Calculate CO₂e, read the total together with the named assessment report. Then inspect the contribution chart. The largest mass is not necessarily the largest source of warming. A small refrigerant or switchgear leak can outrank tonnes of carbon dioxide because its GWP may be thousands of times higher. The contribution ranking is often more useful for reduction planning than the headline total alone.
The greenhouse gas CO₂e formulas and unit conversion
For gases with masses and 100-year potentials , total CO₂e is a weighted sum:
Under AR6, using non-fossil methane, the gases available in the form can be written as:
The chart reports each gas share of the total:
Before multiplication, every input is converted to kilograms. One metric tonne is 1,000 kg, one gram is 0.001 kg, one pound is 0.45359237 kg and one US short ton is 907.18474 kg. Because GWP is a ratio, the output uses the same mass basis as the normalized inputs: kilograms of CO₂ equivalent. Dividing by 1,000 produces metric tonnes of CO₂e.
Why methane source changes its multiplier
Methane eventually oxidizes into carbon dioxide in the atmosphere. When methane carbon came from a fossil reservoir, that oxidation adds fossil carbon to the active atmosphere. AR5 and AR6 therefore provide a higher factor for fossil methane. For biogenic methane, or methane from combustion where the associated carbon dioxide has already been reported, using the non-fossil value avoids counting the same carbon twice. AR4 did not publish the same source split, so this calculator uses its single methane value for both choices under AR4.
Why AR4, AR5 and AR6 produce different totals
Global warming potential is a model-based comparison of time-integrated radiative forcing. Scientific estimates evolve as atmospheric lifetimes, indirect effects, background conditions and climate response are reassessed. For example, non-fossil methane is 25 under AR4, 28 under AR5 and 27.0 under AR6 in the factor set used here. Nitrous oxide moves from 298 to 265 and then 273. These changes do not mean the measured mass changed; they mean the conversion weights changed.
Worked example: digester methane, fertilizer N₂O and a chiller leak
Consider a site reporting one year of emissions: 40 metric tonnes of CO₂ from combustion, 2.5 tonnes of biogenic CH₄ from a digester, 0.4 tonnes of N₂O from fertilizer management and 0.015 tonnes of HFC-134a from a chiller leak. With the unit selector set to metric tonnes, the calculator converts those figures to 40,000 kg, 2,500 kg, 400 kg and 15 kg respectively.
Under AR6, carbon dioxide contributes 40,000 × 1 = 40,000 kg CO₂e. Methane contributes 2,500 × 27.0 = 67,500 kg CO₂e. Nitrous oxide contributes 400 × 273 = 109,200 kg CO₂e. HFC-134a contributes 15 × 1,530 = 22,950 kg CO₂e. The combined result is 239,650 kg CO₂e, or 239.65 metric tonnes CO₂e.
The example shows why mass alone can be misleading. Carbon dioxide represents more than 93% of the emitted gas mass but only about 17% of the CO₂e total. Nitrous oxide is less than 1% of the mass yet contributes about 46% of the warming total. The 15 kg refrigerant leak contributes nearly 23 tonnes CO₂e. Repairing that small leak could therefore matter more than its physical size suggests.
AR6 factors and contributions in the worked greenhouse gas example
| Gas | Mass (kg) | GWP100 | CO₂e (kg) |
|---|
| CO₂ | 40,000 | 1 | 40,000 |
|---|
| CH₄, non-fossil | 2,500 | 27.0 | 67,500 |
|---|
| N₂O | 400 | 273 | 109,200 |
|---|
| HFC-134a | 15 | 1,530 | 22,950 |
|---|
Assumptions and limitations of this CO₂e estimate
This calculator uses 100-year global warming potentials. It does not mix in 20-year factors, temperature-based metrics or sustained-emission metrics. A 20-year comparison would give methane substantially more weight, but combining horizons inside one total would make that total difficult to interpret. Always state the horizon and assessment report beside a published result.
The form converts gas masses that the user already knows. It does not derive emissions from fuel consumption, electricity use, travel distance, livestock population or refrigerant charge. It also does not estimate upstream supply-chain effects, avoided emissions, offsets, carbon removals, land-use change or sequestration. Those require separate activity data and accounting rules.
Only one optional fluorinated gas can be included in each calculation. Refrigerant blends such as R-410A or R-404A contain multiple compounds, so a rigorous inventory should split the blend into constituents or use an authorized blend factor. If several individual F-gases were emitted, calculate them separately and add their CO₂e contributions outside the form.
GWP factors are point estimates and carry scientific uncertainty. Measurement uncertainty in the original gas masses can be equally important. A result displayed to two decimal places is not evidence that the underlying inventory is known to that precision. Keep source records, measurement methods, reporting boundaries and factor references with any figure used for decisions or disclosure.
This page is an educational calculation aid rather than a compliance determination. The applicable reporting standard decides which sources are in scope, whether biogenic carbon dioxide is reported separately, which IPCC report applies and how recalculations of a historical baseline should be handled.
Common questions about greenhouse gas CO₂e conversion
What does CO₂e mean?
CO₂e means carbon dioxide equivalent. It converts unlike greenhouse gases to the mass of carbon dioxide with an equivalent time-integrated warming effect under the selected GWP framework.
Which assessment report should I select?
Select the report required by your program or existing baseline. If no rule applies, AR6 provides the most recent factor set offered here. Do not silently change factor sets in the middle of a trend series.
Why can a few kilograms of F-gas dominate the result?
Fluorinated gases can have GWP values in the thousands or tens of thousands. One kilogram of AR6 SF₆, for example, represents 24,300 kg CO₂e, so careful leak records are important.
Can I enter negative emissions or removals?
No. The fields accept non-negative direct emissions only. Removals and offsets have different permanence, ownership and accounting requirements and should not be subtracted here.
Does the calculator store my inventory?
No inventory data is sent or stored by this page. A share link places the entered values in the URL, so review the URL before sharing it if the figures are sensitive.
Sources. The 100-year factors are drawn from the Greenhouse Gas Protocol publication “IPCC Global Warming Potential Values,” version 2.0, August 2024, which presents AR4, AR5 and AR6 values side by side. AR6 values used here include CO₂ 1, non-fossil CH₄ 27.0, fossil CH₄ 29.8, N₂O 273, HFC-32 771, HFC-125 3,740, HFC-134a 1,530, HFC-143a 5,810, HFC-23 14,600, PFC-14 7,380, NF₃ 17,400 and SF₆ 24,300. Confirm the required factor table with the framework governing your inventory.