Miniature sizing tool?

[Lost Egg]

@eilif - That's a really simple solution, might have to try that.

[carlos marighela]

Good to ask this question here rather than of a wife or significant other, lest hurt feelings be engendered. 

[Aethelflaeda was framed]

Measure your thumb.  memorize it.

[Golgotha]

Green Stuff World does a maybe useful cutting map with scale drawings see: https://www.greenstuffworld.com/en/inicio/618-scale-cutting-mat-a4.html

[Condottiere]

There used to be a thing called The Scale Card, available in different versions, but it's OOP.

The Scale Card is a credit card size tool for every model builder who wants to keep everything in scale. Easy to use at swap meets, flea markets, antique shops, even hobby shops, and at home on your workbench. Using figures (or heads) in scale and three inches of scale rule, it keeps your purchases within your selected scale. Cards range from 1:12 to 1:700, some in metric.