Jessica,
Here is a good sizing chart to go off of for the Demonia boots. I am fully endorsing Redemptionklothing.com as a source for these- the website below is ONLY being mentioned for the sizing chart.
A men's US size 3 would be a women's US size 5. Basically to convert a male shoe size to women's (in US units), take the shoe size and add 2. Demonia states though that their boots run a bit small so keep that in mind when ordering.
Hope that helps!
-Jeremy