LED Series Resistor Calculator
Calculate a resistor for a single LED or identical LEDs in series. Compare the ideal resistance, next E24 value, nominal current and resistor power rating locally.
R = (Vs − N × Vf) / I
P = (Vs − N × Vf)² / R
Range: supply 0.1–60 V; forward voltage 0.1–10 V; 1–100 identical LEDs; target 0.1–1000 mA; calculated resistance at least 0.1 Ω.
Result
Next E24 resistance
150 Ω
E24 is rounded upward. Current assumes exact nominal resistance and a constant LED forward voltage.
- Ideal resistance
- 150 Ω
- Nominal current with E24
- 20 mA
- Voltage across resistor
- 3 V
- Resistor dissipation with E24
- 0.06 W
- 2× dissipation
- 0.12 W
- Suggested standard power rating
- 0.125 W
For one DC series string only. Resistor tolerance, supply variation and LED temperature change the real current. Check the LED ratings and thermal derating; each parallel string needs its own current limiting.
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