If you look at my other reviews, you'll note I have 18" circumference calves at the widest point, with average sized ankles.  I purchased these as a size 9.5 in both brown and black because I have such a hard time finding boots to fit my wide calves.  (To provide a cross-reference on sizing, in Danksos I wear a 41, Birkenstocks a 40.)

These boots fit perfectly as I expected them too.  They are true to size for the foot, and I believe I'll be able to wear skinny jeans tucked into the boot as well.  I did have to allow an amount of time to stretch the boot by wearing them around the house first.  I may have to do this again in the Winter, the first time I wear thicker socks.  (So what this means is that my 18" calf circumference is about as wide as I think anyone should try to fit into these boots--while I'm going to be just fine with my thick socks and/or skinny jeans, I think over 18" wide calves and 9.5 sizing would not be able to zip up the boots.)

One thing to be aware of, especially for those with wider ankles, the ankle sizing is very generous.  I don't mind this, I like the rather casual/rugged styling, it's right at home for the Pacific Northwest.  For those with very small calves and ankles, I could see where they would just be flip-flopping around in these boots.  These are not at all dress boots, but great for slightly up-styling the way that we Pacific NW folks like to do!

As always, fabulous Keen craftsmanship and comfort--I could stand in these all day!  (Stood in these at work for 4 hours straight without any issue.)

Great boots, glad I got both brown and black.  If you have similar calve sizing as I do, and like a more casual, crossover to "outdoorsy" boot, this would be a good option for you too.