These Size Similar To
The Vivobarefoot Primus Lite III run a little long and size similar to barefoot shoes from Be Lenka and TYR. You'll want to make sure you read That Fit Friend reviews and other review comments about sizing these correctly.
How I Suggest Sizing These
These have a wider forefoot and a low-profile upper construction. They should work for a wide range of foot anatomies, but again, they do run long for most. They don't come in half-sizes sans the 12.5...lucky 12.5ers.
If you have narrow and medium-width feet, size these true to size. If you're in-between sizes, go down.
If you have EE+ width feet, size these true to size. If you're in-between sizes and typically close to the end of your toe box, then go up. If not, and you like a snugger-fitting shoe, then go down.
If you traditionally don't have much room at the end of your toe box and you in-between sizes, then you'll want to automatically go up a half size, too.
Check Out: Vivobarefoot's Sizing Chart