Since MBT was sold and closed, MBT shoes changed completely in models and country of manufacture. MBT nowadays is simply a different product.
Therefore you cannot compare the size charts of kyBoots with MBT.
You should take a measurement of your feet as described in our sizing charts and use that exclusively. This is the only way to be certain of your kyBoot size.
The same foot measurement can sometimes be 3-4 sizes apart in MBT, hence irrelevant for comparison.