If you take a first look at the column that reads component dimensions, you might be wondering what 0201, 0402, or 03015 means. Those 4-digit or 5-digit codes are the component size codes, where the first 2 digits of the code stands for the length of the component, and second 2 digits or 3 digits refers to the width.

However, there are two different measurements when it comes to the component size code: metric and inches. When inches measurement is adopted, the size code 0402 means the component size being 0.4'' x 0.2'' (1.0mm x 0.5mm). And when metric measurement is adopted, the size code 0402 means the component size being 0.4mm x 0.2mm. 

Normally, which measurement is adopted would be written in advance, but sometimes they can be really confusing because they might be mixed up. For example, you might see 0201 ~ 200 x 125 as component dimensions in a SMT machine parameters, where 0201 means 0.2'' x 0.1'' (0.6mm x 0.3mm), while 200 x 125 means 200mm x 125mm.

In order to verify if the component size code is in metric or in inches, here are some unwritten rules of it: the most size codes are in inches, while the only exception is 03015 meaning 0.3mm x 0.15mm.

Here is the component size chart: