Rossignol X9 boots are sized using the EU standard. The X9 Boot fits similar to 100mm width boots which cooresponds to B & C foot widths using a foot measuring device.

EUR  US Men   US Women
36           4               5
37         4.5            5.5
38         5.5            6.5
39          6               7
40          7               8
41        7.5            8.5
42        8.5            9.5
43       9.5             10
44       10              11
45       11            11.5
46     11.5           12.5
47     12.5           13.5
48     13.5             14