Most people wear a varied range of sizes amongst brands.
Please refer to the size suggestion in the listing of the shoe (BELOW the size selector).
Your size range typically gives insight to the needs of your feet.  For example, your smallest size typically indicates your length, while the largest size you wear can give insight to the movement or volume of your feet.
Our size recommendations by style are guided by the pattern of the shoe and what keeps them most comfortable and secure.
***EU size/ US size/ UK Size/Length of insole***
35EU/5-5.5US/2.5-3UK/up to 231mm
36EU/6US/3.5-4UKUK/up to 236mm
37EU/6.5-7US/4.5-5UK/up to 244mm
38EU/7.5US/5.5-6UK/up to 249mm
39EU/8-8.5US/6.5-7UK/up to 257mm
40EU/9-9.5US/7.5-8UK/up to 266mm
41EU/10-10.5US/8.5-9UK/up to 271mm
42EU/11-11.5US/9.5-10UK/up to 279mm
43EU/10-10.4US MENS/9.5-10UK
44EU/11-11.5US MENS/10.5-11UK
45EU/12US MENS/11.5UK
46EU/13US MENS/12.5UK
To be honest, the length measurement is not truly the best indicator of your shoe size as each foot has such 3dimensional needs.
If you would like the length to compare, then the best way to measure your feet at home is to tape a piece of paper on the floor against a wall (avoid wall molding).  Stand with your heel firmly against the wall and have someone else mark the tip of your longest toe.  Measure the end of the paper to the mark.
When measuring the length of your feet, keep in mind a comfortable fit is 3 dimensional, not just length.  The diference between sizes can be as little as 5mm so it is best to have someone else measure you instead of doing yourself to minimize error.
Typically if one measures in length smaller than the size they typically wear, it could be for a variety of reasons:
1-incorrect measuring (very difficult to measure one's self correctly and there is as few as 3mm difference in length between sizes
2-While you measure a particular size in length, the volume that your foot needs is of the size you typically wear.  In that case, I would recommend going with the smaller of your "off the rack" size.  For example, if you usually wear an 8.5 or 9 US, then you should order a 8.5 or 39 (8-8.5) with my shoes. 
When in between, it depends on the style and leather you choose, just email me and let me know which you are thinking about. My shoes are made with no stitching in the uppers, allowing for the leather to form to your feet.  There is also no heel and toes stiffener so your toes can be comfortable til the very end of the shoe.  
A snug fit initially is best to allow the leathers to mold to your foot.
Unless you wear a size Wide off the rack we do not typically recommend it. But many people do go thru their whole lives inadvertantly sizing up for their width by going up a size altogether.  While this is fine for shoes with stiffeners, shoes with no stiffeners should be snug for a proper fit.
If you find that your length is actually a size smaller than you ever wear, then I would recommend that size lasted wide. For wide lasting, we add some volume to our shoe molds at the width and towards the toes. Essentially, the leather has more volume across the width, but not necessarily wider footbed (much like a sock).

If you find that your length is in the small end of the size range you sometimes wear, then chances are that size lasted normally is fine as my shoes are made with no toe and heel stiffeners, so your feet are quite comfortable with a very snug fit. Most of my shoes are also unlined, so the leather should stretch as needed.

If your length agrees with the size you typically wear, then order your size as usual.