Measuring your feet is the best way to be clear on what ski boot will fit you.If you want to achieve a comfortable and well fitted ski boot, knowing your foot's shape and dimensions gives you the best reference to compare to a boot shell.
How to measure your feet at home:
Start by tracing your foot on to a piece of paper. From here you can see a great outline of the foot shape. Compare the shape of your foot to the shape of a ski boot shell to find a good match.
You can use a ruler or tape measure to accurately measure your foots length in cm and width in mm.
What Length are your Feet?
Your foot's length (in cm) is crucial in choosing which mondopoint size of boot will fit you. -Remember your foots length in cm equals the mondopoint size of boots you should look at!
What Width are your Feet?
Your foot's width (in mm) will determine which last dimension or boot width you need to look at. -Remember that boot width scales up and down in size from a mondopoint size 26/26.5.
Foot Volume
Then you should take a measurement of the instep. This is the cm measurement from one side of the heel over and around the ankles to the other side of the heel. This will let you know your instep height. You will need to be focused on this if you have a large instep height as this will greatly effect your ski boot choice.
(A regular instep height will match the foot length in cm)
Arch Type and foot Mobility
A little more advanced, but knowing this is helpful in selecting a footbed to stabilize your feet and give you the best comfort in your ski boots.
LOW
MEDIUM
HIGH
What to do with these measurements?
From these measurements you can deduce which types and sizes of ski boots will work for your feet.
Here I go through Ski Boot Sizing.
And here I go through how to check if that ski boot fits you properly with Ski Boot Shell Fitting!