LED Resistor & Voltage Divider Calculator
Find the current-limiting resistor for LEDs (single or in series) with the nearest standard E12 value, or calculate a voltage divider's output.
How to use
- 1Choose LED resistor or voltage divider.
- 2For LEDs, enter the supply voltage, LED forward voltage and current. For a divider, enter Vin, R1 and R2.
How it's calculated
LED: R = (Vs − n × Vf) ÷ I; power = I² × R. Divider: Vout = Vin × R2 ÷ (R1 + R2).
Frequently asked questions
What forward voltage does my LED have?
Typically red ~2.0 V, yellow/green ~2.1 V, blue/white ~3.0–3.3 V. Check the datasheet.
Why round up to a standard resistor?
A slightly higher resistance means slightly less current, which is safer for the LED.
Can a voltage divider power a device?
Only very light loads — any current drawn changes the output. Use a regulator to power circuits.