Hunter boots claim most of their shoes run pretty much true to size, whether you wear them with thin or thick socks. But sometimes you might find the calf might be small while the insole fits perfectly. Hunter also recommends if you are in-between size, you should go a half size down.
For more details about Hunter boot sizing, check the link that I have mentioned earlier. You will find the US, UK, EU, and JP sizes; you can choose any of your desired one.