You need to know the index of refrection of the metal AND the substrate. (You didn't mention the substrate, but I assume your 10nm-thick film is not floating in space!!)
This is a three-layer structure: Air, thin film, substrate. You need to know wavelength, the incident angle, the refractive index of all three layers, and the thickness of the film. With those parameters in hand, you can do the calculation.
The calculation is conventionally set up using the transfer matrix method. You can find many programs online. (This page alone has 2 programs, plus links to 9 others on various different websites.) But with only three layers, the formula is sufficiently simple that you can probably do the calculation more quickly by hand.