Vintage is the wild wild west when it comes to sizing.
As good as suppliers can be at letting you know how an item will fit, without fail every stack I get my hands on there are a few sizing surprises in there.
The whole idea with vintage is you want it to fit oversized. But it's not as simple as buying a size up.
Depending how old the gear is, something tagged XL might fit like a traditional L or even a long M.
On each of our products description we have our recommended sizes.
Go off those.
Here's a simple guide to base your next purchase over;
A Men's AS Colour L fits - Chest: 56cm Length: 78cm
So if we recommend something fits L, that's the measurements (roughly).
If we say XL, it fits bigger than that. And so on.
Vintage varies on length, the bigger sizes often getting boxier rather than taller, but more or less this is the model we use.