What measurement is a tin???
A can. But of what?
Are you referring to a specific recipe? It would help to know the context of your question.
A (tin) can will vary in size. For instance, tomato products commonly come in 14.5 or 28 oz size, and manufacturers love to reduce sizes and keep prices unchanged. To further complicate this, 'tin' woud most likely be used by someone who does not live in or originate from the US, and may use cans that have different sizes than the US. Recipe writers would help us by giving specific sizes, in ounces, grams, cups, litres, or whatever works!