Or: using multiples of 71 for fun and profit.
Why 71? Well, you know how a standard US 12-oz bottle is 355 mls, which is 5×71, whereas an imperial pint is 568 mls or 8×71? Well, you do now. And you know how 14 71s is 994, meaning that an imperial pint is near as dammit 8/14s or 4/7s of a litre? Well, thank me later.
You can probably see where I’m going with this.
| Third | Half | 330 ml | 12 oz US | 2/3 pint |
500 ml | Pint | |
| Third | = | 2/3 | 4/7 | 8/15 | 1/2 | 8/21 | 1/3 |
| Half | 3/2 | = | 6/7 | 4/5 | 3/4 | 4/7 | 1/2 |
| 330 ml | 7/4 | 7/6 | = | 14/15 | 7/8 | 2/3 | 7/12 |
| 12 oz US | 15/8 | 5/4 | 15/14 | = | 15/16 | 5/7 | 5/8 |
| 2/3 pint | 2/1 | 4/3 | 8/7 | 16/15 | = | 16/21 | 2/3 |
| 500 ml | 21/8 | 4/7 | 3/2 | 7/5 | 21/16 | = | 7/8 |
| Pint | 3/1 | 2/1 | 12/7 | 8/5 | 3/2 | 8/7 | = |
To use, pick one row – or column – and memorise it; you can derive all the rest from it. Either that or print it out.
(As for why you’d want to use it, haven’t you ever wondered how to compare a pint at 6%, a 500 ml bottle at 6.8% and a US 12 oz-er at 9.6%? Now you know: they’re all exactly as strong as each other.)
UPDATE Removed the ‘US Pint’ entries and added ‘2/3’, that being a measure people reading this are actually likely to see.
Oh Good Ale 
One Comment
Reminds me of how I hated maths at school. Fucked if I understand how to use it. Well I sort of do as I have an O Level Arithmetic from 1972, but I’ll have to cut out, keep and use a calculator. Clever though.