You already know the value of 1 millimeter, right?
Now,
To convert 8 mm into inches, simply multiply the number 8 with the value of 1 millimeter. (i.e., 0.0393700787)
8 mm = 8 × value of 1 mm
On multiplying the number 8 with 0.0393700787, you’ll get the answer of 8 mm into inches.
See this,