Converting yeast amounts from old recipes

A typical conversion I know of is to use 1/3 as much dry yeast as fresh yeast. If we take James McLeod's answer, then a "large" yeast should be replaced with roughly 18 g of dry yeast (close enough to 3 envelopes á 7 g) and a "small" yeast cake should be replaced by 0.2 ounces dry yeast, or 5.6 g yeast (most recipes will tolerate a full 7 g envelope).

I grew up in the 80s and 90s with 42 g cubes of fresh yeast, if you have a recipe for one of these, use 14 g dry to replace. Sadly, I don't know of any way to make sure whether a recipe refers to the sizes James McLeod's answer uses, or the 42 g size - you will have to take your best guess based on the time and place the recipe was written down.

This is short for “1 large cake of yeast.” According to this investigation, cakes of yeast traditionally came in two sizes:

• Small, around 3/5 of an ounce
• Large, around 2 ounces

This similar recipe gives the substitution “1 large yeast or 3 envelopes dry yeast.”’