Resistors, Capacitors, and more
There are various physical sizes of surface mount resistors and capacitors in addition to the electrical sizes and it can cause quite the confusion initially. First off, a surface mount device (SMD) replaces traditional through-hole components to dramatically reduce the size of PCBs. Surface mount parts have no or short leads, which makes the components smaller but harder to work with.
I recommend using the smallest SMDs that you can for your project to reduce the size of the board. Each SMD is classified by its physical size and electrical value. For example, an 0603 1 kOhm resistor has a physical size of 0603 and a 1kOhm resistance. A summary of the various sizes of components is shown in the picture below from Wikipedia (Thanks to user Zerodamage). Each outline is compared to the scaled dimensions of each side. Notice how small the components get as well as the confusion that imperial code and metric code have the same numbers for different sizes! Make sure you know which your components are using! Any mention of SMD sizes will be imperial throughout the website. I recommend the beginners use 0603 or larger for their first designs. Also, make sure your currents do not exceed the maximum power. Some regulators will require larger components to ensure a small fire doesn't start on your board!
I recommend using the smallest SMDs that you can for your project to reduce the size of the board. Each SMD is classified by its physical size and electrical value. For example, an 0603 1 kOhm resistor has a physical size of 0603 and a 1kOhm resistance. A summary of the various sizes of components is shown in the picture below from Wikipedia (Thanks to user Zerodamage). Each outline is compared to the scaled dimensions of each side. Notice how small the components get as well as the confusion that imperial code and metric code have the same numbers for different sizes! Make sure you know which your components are using! Any mention of SMD sizes will be imperial throughout the website. I recommend the beginners use 0603 or larger for their first designs. Also, make sure your currents do not exceed the maximum power. Some regulators will require larger components to ensure a small fire doesn't start on your board!
In summary, using 0603 (Imperial) for all your components is a safe bet for low power applications. For most resistor electrical values, 0603 can satisfy up to 0.25 W if you buy the correct components on the distributers website.