Page 65 - Make Your Own PCBs with EAGLE from Schematic Designs to Finished Boards

FIGURE 3-4 SMD resistors.

The four digits of the package size actually specify the dimensions of the device. The first two
digits are the length, and the second two are the width. In both cases, the measurements are in 1/1,000
of an inch. Thus a 0402 device has a length of 4/1,000 of an inch and a width of 2/1,000 of an inch.

Now is a good time to introduce the unit called the mil. A mil is not to be confused with a
millimeter (mm). A mil is 1/1,000 of an inch and is still used widely in the electronics industry.
Things get confusing because in electronics you will find some things in American measurements

(mils and inches) and other things in metric units (e.g., 5-mm LEDs). When you come to laying out
your board, you will use mils as the main unit, and most through-hole components have lead spacings
in mils, often 100 mils (0.1 in.).
Table 3-2 shows the most common SMD resistor sizes.

TABLE 3-2 Common SMD Resistor Packages