Check the resistor color bands and use a resistor color code chart
Read the printed value if it is a surface-mount resistor
Measure the resistance with a multimeter set to ohms
Use Ohm’s law: R = V / I
Use circuit requirements and desired current or voltage drop to calculate the needed resistance
Refer to the circuit schematic or component list
Compare with standard resistor series values such as E12, E24, or E96