So far I have sold my 2 pair of wesco boots and one pair of dehner boots, all of them didn't fit my foot well when I walk on the street. Thanks for my friend Henry's chat, and some information on the internet. I have came up some information on how to determine a boot size.
How to try your boots in a store?
1. Go to store in the afternoon. During your feet will be the largest at this time;
2. Wear both boots, not just try on your left foot or right foot;
4. Try in a carpet floor;
5. When feeling your boots, standing not sitting there. In my opinion, you should also walk a bit, maybe for 10-20min, so you know how's the feel, if just wear it for 5min, maybe you won't even feel a thing.
Is that my right boot size?
1. Whole feelings:
You should feel snug except your heels.
2. About your heel:
At the beginning you may feel there is a gap between your feet and the heel of the boots. As you wear more often, the leather heel will gradually fit to your feet size, and you will more the gap is closing day by day. So don't worry if you feel not tight in the heel area. That's normal;
3. About the ball of your foot( the widest part of your foot):
It should sit on the widest part of the sole of your boots.
For some detail explanation, please read these two articles:
Why Heel-to-Ball Is Essential
http://glenviewchiropractor.com/chiropractic-care/measuring-feet
Is a bad shoe fit causing you pain?
http://blog.lwshoes.com/health-fitness/364/
4. About instep:
You should feel tight between the arch of your foot to your boots. But in my opinion, I think a regular snug feeling is enough. I have one wesco boots before, which is extremely tight around instep, so when I was wearing it on the street, just around 15min, my feet feel hurt. And I cannot walk any longer with my boots in this so tight situation.
5. What if my one foot is larger than the other foot?
It's perfectly normal for people have two different foot size, choose the larger size of your foot.
What if I cannot try them on local store?
Go with your normal sneaker/shoe size first, can add 1/2 size larger than your sneaker size. For me, I'd prefer to buy large width boots, as the ball of my foot is quite large, so a EE or EEE is better for my foot.
What about Brannock device?
I actually bought one Brannock device for 70usd, and trying to find out my true size. Lots of people said that that's the best device to see your foot size. I have to say it's just half true about it. As each manufactor has differnt standard on their own size, so even you have your true size, their “size” standard may differnt from your size.
This is extremely true even in those famous brand sneakers such as Nike or Addidas, even the same brand, sometimes different style of sneaker has slight diffferent size. so the best solution is to try it yourself.
Also, you can read this from stompersboots website, it's quite useful in determine boot size:
http://stompersboots.com/boot-fit-guide/