I bought a pair of these previously from another seller and had a nightmare experience. I bought using their chart, which is the same chart  used by this current seller.

As a true size 13, I was told by the first seller the Large boots would fit. They were advertised as 12 - 13. They were really 11.5! Learning my lesson I tried to return them and the other seller forced me to use the Amazon A-Z a guarantee. Then I found this seller. Same great boots and lower price with Prime shipping. This time I ordered the XL, listed as size 14. They're perfect 13's. I think to get a proper fit, if you're in a bracket like 12-13, you need to go bigger. You can always put inserts in the boot to cut the size down.