About this project
A working prototype for applying a carbon price to everyday purchases — voluntarily, at the level of a single household, without waiting for national policy.
The idea
Economists broadly agree that putting a price on carbon is the most efficient way to reduce emissions. It keeps failing politically. Carbon taxes are hard to legislate, easy to campaign against, and frequently repealed.
Meanwhile, a large number of companies already run something called internal carbon pricing: they charge their own business units a notional price per tonne of CO₂, so that investment decisions internalise a cost the law does not yet impose. It is voluntary, self-administered, and it changes behaviour.
This project asks a simple question: why should that be limited to corporations? If a company can impose a carbon price on itself, so can a household. This calculator is what that looks like in practice — you pick the price, and every product you look at is quoted at price plus carbon charge.
What makes it different
There is no shortage of tools that report a footprint in grams or kilograms of CO₂e. The difficulty with a number in grams is that it does not tell you what to do: you are left holding two incomparable quantities, a price and a footprint, and no exchange rate between them.
Converting the footprint into money supplies that exchange rate. Once carbon is expressed in the same units as price, the two collapse into a single figure, and the decision becomes one-dimensional — the cheaper total is the better choice on both counts at once. That conversion, rather than the footprint estimate itself, is the point of this tool.
What stage this is at
This is a beta prototype, published openly so the method can be examined and criticised. The emission figures are illustrative category averages, not certified product footprints, and the methodology page documents their limitations in detail rather than burying them.
The current version searches the Japanese Rakuten Ichiba catalogue, because the underlying emission data — Japan's 3EID input–output dataset — is published for that economy. A US version using EPA's USEEIO factors is in development.
Who built it
The calculator is built and maintained by an economist working on carbon pricing, as the practical counterpart to a working paper on extending internal carbon pricing from firms to households. The category-to-sector mapping, the method, and the code are the author's own work.
It is an independent project. It is not affiliated with, endorsed by, or sponsored by Rakuten, the National Institute for Environmental Studies, or any of the organisations whose published carbon prices are cited as reference points.
The wider project
This calculator is one part of the Virtual Carbon Pricing project, which collects resources for individuals and organisations wanting to apply carbon pricing to themselves. More at sites.google.com/view/virtualcarbonpricing.
Feedback
Corrections to the method are genuinely welcome — particularly on the mapping from retail categories to input–output sectors, which is the part most open to challenge. Contact details are on the project site.