Women's would be 1 1/2 bigger than men's so... 11 1/2 is your size in women's if your men's is 10.
Add 1.5 to 2 sizes. For example, if I wear a women's 10, I would try a men's 8.5 or maybe 8. Mens shoes tend to run wider than women's so that may affect your size.
Probably a size 7 or 6 in men's shoe sizes. Men's feet tend to be a little bit wider and taller than women's.
as for the shoes size conversion, you can refer to this shoes Size Conversion Tableat http://www.fulljordan.com/Column9.aspx
You will wear size 4.5