The assumption is that for each product that we make out of recycled paper or bamboo (which hasn’t required a new tree to be cut down just for that toilet paper), then one less ‘traditional’ product needs to be made (and as such, less trees need to be cut down). 

We don’t know for sure how many less trees are cut down just to make toilet paper, so when we talk about trees saved, we talk about the equivalent number of trees. 

We’re not just making those numbers up - we base it on some pretty sound assumptions.

Trees aren’t a standard unit of measure, so we use the average size of a softwood pine tree - a tree frequently used to make toilet paper. Pine trees are usually cut down at 12-15 years, when they reach 7 inches (almost 18 cm) wide, and 40 feet (just over 12 metres) high.

We then work out how much pulp that tree would make, and how much toilet paper that pulp would make! The pulping method in our assumption is chemical pulping, specifically kraft process.  

We calculate forest density based on the average density of commercial forests (which is 954 trees per hectare).