WORKBENCH 03 / 5 min TO EXPLORE
LED Resistor Calculator
Choose the resistor for your next LED circuit, with the working explained along the way.
- 01 Try an example
- 02 Change one thing
- 03 Understand why
Try it out
Forward voltage and current depend on the exact LED. 2 V and 20 mA are example values, not universal ratings.
Results update as you type. Try changing just one value.
SEE YOUR CIRCUIT
THE IDEA BEHIND THE NUMBERS
A small resistor does an important job.
An LED needs current limiting. A series resistor drops the voltage left over after the LEDs and sets the approximate current. Connect supply positive → resistor → LED anode; connect the LED cathode to supply negative.
The tool rounds up to an E24 nominal resistor value so the nominal current does not exceed your target. It also suggests a power rating with at least twice the calculated dissipation.
What do forward voltage and E24 mean?
- Forward V
- The approximate voltage drop across an illuminated LED. Use the value at your target current from its datasheet.
- mA
- Milliamps. 20 mA is 0.020 A.
- E24
- A series of 24 nominal resistor values per factor of ten, such as 330 Ω, 360 Ω, and 390 Ω.
- Power
- Energy converted to heat each second. A resistor’s wattage rating must exceed the power it dissipates.
Leave room for real components.
Forward voltage, supply voltage, and resistor tolerance all affect actual current. Verify the worst case before building. This tool models one series string; parallel strings each need their own resistor. For high-power LEDs, use a suitable constant-current driver and thermal design.