Carbon emmisions formula - Reuse

Hi I am looking for a way / a Formula to calculate carbon emission savings (carbon footprint) only by using the REUSE aspect

I am sure that there are many parameters like materials of the item etc but I am after Just a generic formula that takes into account the item's weight

I found the following links not sure if it helps :

Waste hierarchy - Wikipedia, the free encyclopedia

Global Warming Mathematics

Carbon Footprint Calculator - math details on how we do the calculations

I am trying to create a PHP program that will output CO2 savings and Tree Savings (e.g you save x trees) from reuuse.

Sorry I couldn't be more specific and this is a bit vague but any help will be much appreciated