CO2 unit of measurement
Carbon dioxide and the other greenhouse gases are generally measured in metric tonnes (1,000 kg), but kilos and grams can also be used.
What is tCO2e?
Greenhouse gases are typically given as tCO2e – tonnes of carbon dioxide equivalent. The e-standing for equivalent – means that the measurement includes greenhouse gases which aren’t carbon dioxide, converted into equivalent amounts of CO2 based on warming potential.
For example, methane has 28-36 times the global warming potential of CO2, so 1 tonne of methane would count as 28-36 tonnes of CO2e.
Explaning co2e 
to your user
A simple, unobtrusive way of explaining what CO2e is to your users is to add a small info icon the user can hover for additional context:
*CO2e includes all greenhouse gases emitted, converted to the warming power of CO2.”
when to use tonnes, Killos Grames 
Depending on the product or service that you sell, the carbon emissions will vary drastically.
For example, an intercontinental shipment of goods via sea typically emits a few tonnes of COe. Running cloud computing services for a small company emits a few hundred kilos of CO2e. Buying most fruits and vegetables emits a few hundred grams of CO2e.
Keeping 
unit consistent
If you need to display the emissions of products and services in your platform, you should consider a couple things to decide on whether to keep units consistent, or to mix them:
- The relative scale of emissions
- Whether it is important to compare emissions.
If the scale of emissions you need to display is relatively consistent (mostly in the tonnes, kilos, or grams range), or you need to make emissions comparable, consider keeping the unit consistent.
Mixing units 
On the other hand, if the scale of emissions you need to display varies significantly (spanning 4 orders of magnitude or more), and comparing emissions isn’t key, consider using the most appropriate unit for each value.
