Ipc-7351c Pdf Link -

In the 1990s, the electronics industry faced a quiet crisis. Every component—a resistor, a microchip, a connector—had a "land pattern." This is the copper footprint on a circuit board where the component sits and gets soldered.

Many CAD tools like Ultra Librarian or Library Expert use IPC-7351 equations to automatically generate compliant footprints for you. ipc-7351c pdf