LED Resistor Calculator
Calculate the correct series resistor value for an LED circuit given supply voltage, LED forward voltage, and desired current.
Circuit Parameters
V
Common values: 3.3 V, 5 V, 9 V, 12 V
V
Quick:
mA
Typical range: 5–30 mA. Check your LED datasheet.
Results
Fill in the values above and click Calculate.
Exact Resistance
Nearest E24 Standard Value
Use this value in your circuit
Actual LED Current
With the standard resistor
Power in Resistor
Recommended Resistor Rating
2× safety margin applied
Formula Used
R = (Vs − Vf) ÷ If
P = If2 × R
Where R is resistance in ohms, P is power in watts, If in amps.
Summary
Calculate the correct series resistor value for an LED circuit given supply voltage, LED forward voltage, and desired current.
How it works
- Enter the supply voltage of your circuit (e.g., 5 V for USB, 12 V for automotive).
- Enter the LED forward voltage — found on your LED's datasheet (typically 1.8–3.5 V).
- Enter the desired LED current in milliamps (common values: 10–20 mA for standard LEDs).
- The calculator applies Ohm's Law: R = (Vs - Vf) / If.
- It then recommends the nearest standard E24 resistor value and minimum power rating.
Use cases
- Selecting a resistor before soldering an LED to a breadboard or PCB.
- Verifying an existing circuit design before powering it on.
- Quickly comparing resistor needs for 3.3 V, 5 V, and 12 V supply rails.
- Teaching electronics — visualizing Ohm's Law in a real-world LED context.
- Protecting high-brightness LEDs running at lower currents to extend lifespan.
- Calculating resistors for multiple LED colors with different forward voltages.
Frequently Asked Questions
Last updated: 2026-06-13 ·
Reviewed by Nham Vu