There are 1000000 nanometres in one millimetre. Therefore, to convert millimetres to nanometres, multiply by 1000000. For example, 13 millimetres is equal to 13 x 1000000 = 13000000 nanometres.
There are 304.8 millimetres in one foot. Therefore, to convert feet to millimetres, multiply by 304.8. For example, 3 feet is equal to 3 x 304.8 = 914.4 millimetres.