What Resistor Do I Need for an LED? Formula and Quick Chart
Quick answer: R = (supply voltage - LED forward voltage) ÷ desired current. For a red LED (2 V) on 5 V at 10 mA: R = (5-2)/0.01 = 300 Ω — use the next standard value, 330 Ω.
The Formula
R = (Vs - Vf) / If, where Vf and the rated current come from the LED datasheet. Typical indicator current is 5-20 mA; low-current LEDs work at 2 mA.
Quick Chart (10 mA target)
| Supply | Red 2.0 V | Green 2.2 V | Blue/White 3.2 V |
|---|---|---|---|
| 3.3 V | 130 Ω → 150 Ω | 110 Ω → 120 Ω | 10 Ω → 12 Ω |
| 5 V | 300 Ω → 330 Ω | 280 Ω → 300 Ω | 180 Ω → 200 Ω |
| 12 V | 1.0 kΩ | 980 Ω → 1 kΩ | 880 Ω → 910 Ω |
Do Not Forget Power
P = I² × R. At 12 V and 20 mA the resistor dissipates about 0.08 W — a 0.25 W part is fine, but at higher currents or voltages step up to 0.5 W.
Common Questions
- No resistor at all? The LED draws excess current, overheats and dies quickly.
- LED too dim? Lower the resistance, but stay below the rated If max.
- Several LEDs? Series LEDs share one resistor (add their Vf); parallel LEDs each need their own.
Need datasheets, samples or a bulk quote? Browse our LED datasheet center or product center. Hongcheng Optoelectronics, a member of Guangyu Group, has 20+ years of LED packaging experience with A-grade chips and 99.99% pure gold wire bonding.
Share
