Earlier quoted context omitted.
They are multiplying the size of a wine glass by the ABV of red wine, the size of a shot glass by the ABV of vodka, the size of a pint glass by the ABV of beer... it's all estimation, but it's what they've got.
But you just defined what a "standard drink" is, no? All of those values are supposed to be equal: 5oz of wine * 12% = 1.5oz of spirits * 40% = 12oz of beer * 5% so I'm still confused... Edit: Wait, do you mean the size of a full glass ? That's... an odd way to measure things.
You go to a pub and order a pint of lager. In the UK, that's 568mL, and you think of it as one drink -- even though it's clearly not.
You go to the same pub and order a shot of whiskey, and it's about 1.5oz, so it's the same as you think it is.