Resistor Value
150Ω
Exact
150Ω
Power
60 mW
Standard Resistor Value
150Ω
Exact: 150Ω
Actual Current
20.0 mA
Power
60 mW
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Inputs
Result
R = (5-2)/0.02 = 150Ω. Nearest E24 value is 150Ω. P = 0.02² × 150 = 60mW.
Inputs
Result
R = (12-3.2)/0.02 = 440Ω. Next E24 value is 470Ω. P = 0.02² × 470 = 188mW.
R = (Vsupply - Vforward) / Iled. For a 5V supply, red LED (2V forward, 20mA): R = (5-2)/0.02 = 150Ω. Always use the next higher standard value for safety.
| LED Color | Forward Voltage | Typical Current | Resistor (5V) | Resistor (12V) |
|---|---|---|---|---|
| Red | 2.0V | 20mA | 150Ω | 510Ω |
| Green | 2.1V | 20mA | 150Ω | 510Ω |
| Blue | 3.3V | 20mA | 82Ω | 430Ω |
| White | 3.2V | 20mA | 91Ω | 430Ω |
Too little resistance means too much current. The LED overheats, dims prematurely, and eventually burns out. Even a few milliamps over rated current can halve LED lifespan.
For LEDs in series: R = (Vsupply - N×Vf) / If, one resistor works. For parallel LEDs, each needs its own resistor because Vf varies slightly between LEDs.
P = I² × R. For 20mA through 150Ω: P = 0.02² × 150 = 60mW. A standard 1/4W (250mW) resistor is fine. Derate by 50% for reliability.
Electronics, outdoor, and everyday tools
Last Updated: Mar 20, 2026
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