While it’s a different company I think Bosch can serve as an example on how this can be calculated as they are already “carbon neutral”.

www.bosch.com/sustainability/environment/

At present, we use carbon credits to offset residual CO₂ emissions, such as from combustion processes (heating, process heat). In addition, we refer to carbon credits to offset electricity sourced in countries with only limited availability of green electricity. As we make progress with levers 1 to 3, we want to gradually reduce the share that we offset to achieve carbon neutrality to no more than 15 percent by 2030.