My problem with estimating centimeters is that because I'm in the United States, the only time I use centimeters is in science, and in those cases the actual values they quantify don't really matter, and I end up thinking of centimeters as short inches. However, I've noticed that in my mind I sometimes think of it being about 1.5 centimeters to an inch, not 2.5 centimeters to an inch...
Wait... WAIT. I know the US uses a lot of Imperial units, but do you seriously like not even use cm and m on a daily basis? Like, do schoolkids not have standard 15cm/30cm rulers? Do people not know doorframes are about 2m high? Is it not common knowledge that 1 mile is 1 kilometer, 609 metres, 34 centimetres and 4 milimetres? Okay that last one is maybe not common here either but still, this blows my mind that you guys are using feet and inches for... most things?
Oh yeah, very little metric happens in America. There are some exceptions.
As stated, there are races that are measured in meters. You can buy a 2-liter bottle of soda, but don't expect anyone to figure out how much soda is in 300 milliliters.
Many wrenches are sold in two sets to account for cars (and whatever else) built with metric bolts.
I always hear of street drugs being sold in the realm of grams, but I don't have firsthand knowledge of that. But a lot of medicine lists ingredients in milligrams.
When people aren't up for running a marathon (26.2 miles, I believe), they may sign up to run a 5K or a 10K.
Aside from the scientific community, everyday life in America is almost exclusively imperial measurements. Unless I'm washing down 500 mg of ibuprofen with a 2-liter Coke after running a 5K, Americans would just stare at me blankly if I try to use anything metric.