The UC Berkeley household calculator we use uses income as a proxy to determine total expenses. Then it breaks those expenses into 15 categories (e.g. medical, vehicle services, etc.) to determine the carbon footprint of a dollar spent in each category. These calculations are based on something called the Comprehensive Environmental Data Archive for Economic and Environmental Systems Analysis (CEDA 3.0 Climate). Here's more about that here (see PDF). And here's a deep dive into how the household calculator works (see PDF).
Emissions from supply chains is enormously complicated, but it's also a big source. It's a ball of knots we have to collectively untangle... Walmart for example has the 1 gigaton challenge, where they are facilitating their suppliers to reduce, collectively, 1 gigaton of emissions.
The UC Berkeley business calculator we use takes the same approach as the household calculator. Instead of household income, it uses revenue. That is -- all of the money coming into the organization. Then it uses that revenue number to determine how much money is likely spent on procuring things like paper, chemical products, printing, etc.
For an organization with an income of $700,000, the calculator assumes about $12,000 is used annually to procure things like paper, etc. So this number does not include salaries, benefits, or utilities.