LED resistor on 3.3 V by color (20 mA, E12 values)
| LED | Vf (typ.) | Exact R | E12 resistor | Current | Resistor power |
|---|---|---|---|---|---|
| Red | 2.0 V | 65 Ω | 68 Ω | 19.1 mA | 24.9 mW |
| Orange | 2.0 V | 65 Ω | 68 Ω | 19.1 mA | 24.9 mW |
| Yellow | 2.1 V | 60 Ω | 68 Ω | 17.6 mA | 21.2 mW |
| Green (standard) | 2.2 V | 55 Ω | 56 Ω | 19.6 mA | 21.6 mW |
| Green (bright/true green) | 3.2 V | 5 Ω | 5.6 Ω Not recommended: under 1 V of headroom | 17.9 mA | 1.79 mW |
| Blue | 3.2 V | 5 Ω | 5.6 Ω Not recommended: under 1 V of headroom | 17.9 mA | 1.79 mW |
| White | 3.2 V | 5 Ω | 5.6 Ω Not recommended: under 1 V of headroom | 17.9 mA | 1.79 mW |
Typical forward voltages; check your LED's datasheet. Rounding up to the next standard value keeps the current at or just below 20 mA.
Frequently asked questions
What resistor for a white or blue LED on 3.3 V?
3.3 V leaves only 0.1 V of headroom for a 3.2 V LED, so the current would swing wildly with tolerances. Use a constant-current driver or a higher supply.
How many red LEDs can I put in series on 3.3 V?
As a rule of thumb keep at least 1 V across the resistor: 1 red LED (2.0 V in total) with 68 Ω at 20 mA.
Can I use a bigger resistor?
Yes. A larger value just lowers the current and brightness; most modern LEDs are clearly visible at 5–10 mA.