Resistors are available in different packages. The most popular ones at present are the rectangular surface mount resistors and axial resistor in through hole designs.

The shape and size of surface mount resistors are standardized, most manufacturers use the JEDEC standards. The size of SMD resistors is indicated by a numerical code, such as 0201. This code contains the width and height of the package. So in the example of 0201 Imperial code, this indicates a length of 0.020″ and a width of 0.010″. This code can be given in Imperial or Metric units, in general the Imperial code is used more often to indicate the package size. On the contrary in modern PCB design metric units (mm) are more often used, this can be confusing. In general you can assume the code is in imperial units, but the dimensions used are in mm. The SMD resistor size depends mainly on the required power rating. For surface mount components, the right solder pad size and land pattern are very important. The following table lists the dimensions and specifications of commonly used surface mount packages.

Sometimes surface mount resistors are also used as MELF packages (Metal Electrode Leadless Face). The main advantage of using MELF to take place standard SMD packages is the lower thermal coefficient and better stability. The TCR of thin film MELF resistors is often between 25-50 ppm/K while standard thick film SMD resistors often have a TCR of > 200 ppm/K. This is possible due to the cylindrical construction of MELF resistors. On the other hand, MELF resistors need more space for installation. There are three common MELF package sizes: MicroMELF, MiniMELF and MELF.