If in case you are not sure what nm is, this stands for nanometers. You may want to know how you can convert it to m which is the meter. To do this, you first need to multiply the nm to 1 so that you can easily get the equation that you are looking for.

By doing this, you will get this equation: (640 nm)(1 m / 10^9 nm) will be equal to 640 1 m / 10^9 = 6.4 10^-7 m. If in case you still do not understand how you can do this, there are different applications that you can use that will allow you to make conversions easily.