Bike sizing

I'm looking to buy just a regular shopping bike but I'm not sure of the size. The size I see the most of in the store is 26 so i guess this is average? But the seats on all of them are up too high for me and I can't tell how low it goes.

So my question is, is 26 a comfortable size for someone who is 5'1

The seat will go down to the top of the pole that is underneath the seat and is part of the main bike frame. Ask the shop staff to show you where the seat goes down to- I'm sure they will be happy to do so.

Japanese of all sizes seem to ride that standard sized bike, including tiny obaasans, so you should be okay.

I always thought that 24 was average size for women (which I rode comfortably - I'm 5 feet 2) and 26 was for men. Maybe younger people nowadays have longer legs lol

26 will be high for your height. You can look into foldable bikes as small as 18 inches...

foldables bikes can be found for around 5000 yen..
look on kakaku.com if you can wait a while for it to arrive... or just go to a big box store..