armed with the info from the above posts, I would put a little piece of paper in my wallet with the following calculations: (or whatever sizes fit your desired range)
16 hands = x centimeters
16. 2 hands = y centimeters
17 hands = z centimeters.
Then when someone tells you the horse is 168 centimeters or whatever, you can look at your little cheat sheet and pretty much know what they are. And then you won't need to have the calculator handy!
We don't get less brave; we get a bigger sense of self-preservation........
It's easy....work off the .2s in all height groups:
12.2 = 128cm
It's easy to remember replace the .2 with 8 and you have the figure in cms but to be honest alot of places will talk in hands or cms!!