Metric:
xxx.xx.xx

the units are, (mm).(mm).(N/m)

English:
xxx.xxx.xxx

the units are, (inch).(inch).(lb/inch)

The first number of the series does NOT represent the spring rate. It represents the length of the spring itself. The second number represents the diameter of the spring, and the last number represents the spring rates.

So if you have a number like this,

Front 180.64.61
Rears 200.64.44

that means your springs are labelled in metric units. To convert them to english units (used in the US), you must...

divide the first number by 25.4, divide the second by 25.4, and multiply the last number by 5.7