# Diffraction grating, lines per mm, and how to show the spacing

A diffraction grating is labelled 300 lines mm^-1 (lines per mm)
Show that the spacing (d) between the lines on the grating is 3.3 x 10^-6m

i cant really think of any relevant equations. but i'm assuming standard form. i cant believe that the answer would be as simple as converting to m's from mm's

since there are 300 lines in every mm, i assumed converting to standard for, and metres instead of mm. which might get me close to the answer.

300 lines per mm = 3000 per cm = 3000000 per m = each line 3 x 10^-6 ?

this isnt right, clearly. since the anser is 3.3 x 10^-6, i just cant work out how to show it