For the Americans inches are used every day just as pounds, feet and miles. For the rest of the world we use cm, meter and kilometer. Except the UK who does a mingle mangle of both. On the streets the speed signs are in miles but you have to calculate in km which is written on the car's dashboard. Mostly they have both, otherwise the time you calculate miles in km or the other way around your car may have kissed a tree.
The grandparents are in steady conflict with their grandchildren, because the grandchildren mesure in cm, meters and kilometers while the grandparents are still with their inches, feet and miles ! That's the same with the temperatures.
As 1 inch is 2.54 cm, it is far better to use inches when you measure your waist, it makes you slim !
If your waist measures 60 cm, the number sounds a lot, but if it measures only 24 inches, it is a small number ! That sounds much better and would look better on a paper when you want to be a model. The numbers are not so high and that counts for everything. That's maybe because the Americans keep with their inches, because if they had a waist of 60 that would be 153 cm !
Anyway I have learned at school that inches exist, for the rest I must have slept, because I didn't like Math classes. When I stayed with my aunt in Madison Wisconsin, we never talked about the system of measurements, and I didn't care about how many km or miles we made per day when we travelled or how many inches her cat's tail measured.