Written by Dr. Mark Cucuzzella

In the past three years, I have completely rethought how a shoe should fit. More accurately I now think about how a shoe should fit rather than just pick a size.  Since I started running more true barefoot miles over the last year my foot size has greatly increased in thickness. I can no longer wear any shoe that I owned six months ago.  My Newton running shoe size has increased from 11.5 to 12.5 and my next pair of VivoBarefoot Evos will be a 46.  I had started comfortably in a 44, now wear 45 without an insole and wish there were more room.

At Two Rivers Treads, which just launched an online store to complement our brick-and-mortar store in Shepherdstown, West Virginia, we defy old-school thinking of sizing and narrow-shaped, ill-fitting conventional shoes. Improper shoe sizing and shape are the primary cause of ingrown toenails, bunions, corns, hammer toes, and hallux valgus.  Shoes that don’t fit your feet correctly can also lead to muscular imbalances in the body, leading to foot, knee, and hip injuries.


A proper fit accounts for the natural expansion of the foot upon ground contact. Excess waste is eliminated, along with everything that inhibits your foot’s natural motion. So your foot is free to move and work the way nature intended it to; the way of its own barefoot motion.  Call it toe wiggle freedom.


Yet, with sizing, most get it wrong


The naturally thickened feet of Dr. Daniel Lieberman, Ken Bob Saxton, and Dr. Mark Cucuzzella. Photo taken by Nick Pang at the NYC Barefoot Run sponsored by Merrell.

First, abandon the notion that you have a shoe size. Instead you have a foot size.  Shoes are made all over the world and apply different shapes and standards. If you measure your foot seated with a traditional measuring device like a Brannock Device and base your size on that you will likely be off by 1-2 sizes when applied to a running or hiking shoe.  One shoe size is only 1/3 an inch.


Also critically important is that the Bannock device measures the widest part of the shoe at the ball. Infant feet are widest at the ends of the toes, not the ball of the foot. The natural alignment of the human foot is where the metatarsals directly align with phalanges (toes) and get wider than the ball of the foot.


Here’s why most sizes are too small:

When a load is applied to a foot by running or with a pack weight your foot will spread in length by up to half an inch


You need at least an 1/8 inch or more space on heel and toe for any sock.


You want 1/3 to 1/2 an inch in front of your big toe to allow room for loading and splay

Your foot will splay 15 percent in width under load.


Your foot is widest at the toes and unfortunately most shoes are not shaped this way.


Tips on sizing:


At Two Rivers Treads, we never had a customer return shoes because they too were too big.


Do not assume you are the same size as a previous shoe.


Take your time and try several shoes on, preferably at the end of the day. Go run in them. Do not try them on sitting.


Always try both shoes on. If feet are slightly different size fit the larger foot.


Take the shoe removable insole out and see how your foot fits against the insole as a template. Is there room at the toes or does you foot spill over the insole?  If no room to spare or if your foot spills over this shoe will not fit comfortably.


Keep going half size up until the shoes are obviously too big.


Try on shoes at end of day when feet are most flattened and swollen

Try on with the type of sock you will wear for activity.


For women, you may fit better in a men’s shoe for width.


Do not lace the shoes up tight.  Allow spread in the midfoot and forefoot.


Go up onto the ball of the foot. Can you put your index finger between your heel and the back of the shoe- if not likely too small.


Consider not using the soft insole.  This takes up space in the shoe and interferes with ground feel.


Walk on a firm surface, not a carpeted one.


If you are a runner you must run in the shoe.  What feels nice and soft when walking is the opposite of what you need when running, which is a more firm base to give the message up your kinetic chain to stabilize.


Sandals are great as they allow for natural foot spread without restriction from an upper.



When trying on shoes, wear the socks you would normally wear in them. Socks are not necessary but are mainly for added comfort, especially in avoiding blisters. Like shoes, socks can be too tight, contributing to foot irritation and restriction. For most situations, socks should be thin and not tight.


Make sure your socks do not bunch though.


Thicker winter socks may require a half-size larger shoe.


Which style of socks you wear (low-cut or above the ankle) and what they’re made of (natural fibers such as wool or cotton, or a blend of synthetics) is up to you.



But like shoes, make sure they fit well; and be careful to avoid the sock interfering with shoe fit. My preference is merino wool of light synthetic blend.