Question About Boot Size

The boots have to be long enough to accommodate your feet, comfortable but hold your foot and ankle firmly so that the foot doesn't slide around in the boot. The tips of your toes should not be "bump stops" as Ranchero said the length is relatively unimportant - the boot isn't really doing too much at the toe end other than clamping into the binding and transferring the force you apply through the boot to the ski. Most of that force comes from body weight and position of your body and bar some of that force being applied through the big toe, the other toes themselves are doing relatively little. (In this respect similar to running.)
It always puzzles me when fast bowlers cut holes in their boots for the big toes. Why not just get boots that fit properly - long enough and holding the foot firmly so it doesn't slide in the boot. Obviously ski boots have the advantage of coming further above the ankle to help restrain the foot, but the principal is the same - the ends of your toes should not be the part that stops your foot sliding in the boot.

Blimey. What's Mike done to upset people? I don't think Mike is saying that your boots should be loose. He's merely saying that for most people you don't need a super tight or uncomfortable fit (which I think is sensible). The rough guide he mentions in relation to boot length is a reasonable one (noting that it's a rough guide and therefore not the only factor to consider). And he's recommending the OP to see a boot fitter.

I understand Andymol2's point about the toes not being an "end-stop" for the foot within the boot. One thing, though, that did help me was realising that even though the boot fitted, the liner was a bit short. So I made a little slit in the front edge of the liner to allow my big toe to just peep through. Works.