If you wear a size 10 in women shoes so what size would it be in men shoes?

Not all shoe brands are the same, but for New Balance shoes, which is a good standard of measure:

If you wear a women's size 10 medium (10 B), then your men's size is usually going to be an 8.5 narrow (8.5 B), because the men's and women's scales are offset by 1.5 sizes and by 1 width deviation. A women's medium width is normally "B", while a men's medium width is a "D".

women's:

4A (X-narrow) - 2A (narrow) - B (medium) - D (wide) - 2E (X-wide) - 4E (XX-wide)

men's:

2A (X-narrow) - B (narrow) - D (medium) - 2E (wide) - 4E (X-wide) - 6E (XX-wide)

So if you want to buy a men's shoe in size 8.5, you may want to choose the men's narrow (B) width if it is available. These numbers and letters correspond to the sizing standards of the Brannock foot measuring device.