Depends on the boot, some are too wide for me. Not terrible but leaves room for my foot to slide a little and cause problems in warm weather with lots of long days in a row, and also not ideal in technical terrainI think slightly smaller than true to size for me, and narrower. I always wear 12 Oboz and other boots.
I recently confidently ordered a pair of Crispi Thor II GTX in 12 - too small and narrow, then 13 - too long, then 12.5 - too narrow mid foot, then 12.5 Wide - just right. Probably the first time I've ever felt that there was no leeway .5 sizes up or down.