LED resistor for 12 V
Resistor values for LEDs on 12 V adapters, LED strips, car and motorbike electrics, 12 V lead-acid batteries. The tables use typical forward voltages and round up to the next standard value, so the LED never gets more current than the target. The calculator is preset to 12 V — change the LED or current to suit your part.
12 V LED resistor table at 20 mA
20 mA is the classic rating for 3 mm and 5 mm indicator LEDs. Formula: R = (12 − Vf) ÷ 0.020.
| LED color | Vf | Exact | E12 (up) | E24 (up) | Actual current | Power → rating |
|---|---|---|---|---|---|---|
| Red / orange | 2 V | 500 Ω | 560 Ω | 510 Ω | 19.6 mA | 200 mW → 1/2 W |
| Yellow | 2.1 V | 495 Ω | 560 Ω | 510 Ω | 19.4 mA | 190 mW → 1/2 W |
| Green (traditional) | 2.2 V | 490 Ω | 560 Ω | 510 Ω | 19.2 mA | 190 mW → 1/2 W |
| True green | 3 V | 450 Ω | 470 Ω | 470 Ω | 19.1 mA | 170 mW → 1/2 W |
| Blue / white | 3.2 V | 440 Ω | 470 Ω | 470 Ω | 18.7 mA | 160 mW → 1/2 W |
12 V LED resistor table at 10 mA
Modern LEDs are bright at 10 mA or less, and half the current doubles the resistor value and halves its heat.
| LED color | Vf | Exact | E12 (up) | E24 (up) | Actual current | Power → rating |
|---|---|---|---|---|---|---|
| Red / orange | 2 V | 1 kΩ | 1 kΩ | 1 kΩ | 10 mA | 100 mW → 1/4 W |
| Yellow | 2.1 V | 990 Ω | 1 kΩ | 1 kΩ | 9.9 mA | 98 mW → 1/4 W |
| Green (traditional) | 2.2 V | 980 Ω | 1 kΩ | 1 kΩ | 9.8 mA | 96 mW → 1/4 W |
| True green | 3 V | 900 Ω | 1 kΩ | 910 Ω | 9.89 mA | 89 mW → 1/4 W |
| Blue / white | 3.2 V | 880 Ω | 1 kΩ | 910 Ω | 9.67 mA | 85 mW → 1/4 W |
LEDs in series on 12 V
The most LEDs one resistor can serve while still leaving at least 1 V across it (so the current stays predictable), with the resistor for 20 mA. Efficiency is the share of supply power that reaches the LEDs.
| LED color | Max in series | LED voltage | Resistor (power) | Efficiency |
|---|---|---|---|---|
| Red / orange | 5 | 10 V | 100 Ω (40 mW) | 83% |
| Yellow | 5 | 10.5 V | 75 Ω (30 mW) | 88% |
| Green (traditional) | 5 | 11 V | 51 Ω (20 mW) | 92% |
| True green | 3 | 9 V | 150 Ω (60 mW) | 75% |
| Blue / white | 3 | 9.6 V | 120 Ω (48 mW) | 80% |
When the supply is not exactly 12 V
Current with the 20 mA resistor from the table above (510 Ω for red, 470 Ω for white) at the voltages this supply really sees:
| Condition | Supply | Red LED | White LED |
|---|---|---|---|
| Battery, engine off | 12.6 V | 20.8 mA | 20 mA |
| Nominal | 12 V | 19.6 mA | 18.7 mA |
| Car, alternator charging | 14.4 V | 24.3 mA | 23.8 mA |
Notes for 12 V circuits
For a 12 V wall adapter the nominal value is fine. In a car, design for the charging voltage instead: with the engine running the alternator holds the system at roughly 13.8–14.4 V, and a resistor chosen at 12 V lets about a fifth more current flow (more for blue and white LEDs, because a smaller voltage is left across the resistor). Vehicle electrics also carry spikes, so automotive LED circuits often add a series diode for reverse-polarity protection and a TVS diode — subtract about 0.7 V for a silicon diode when you size the resistor.
One LED on 12 V wastes most of the power in the resistor. Three red LEDs (6 V) or three white LEDs (9.6 V) in series use the voltage instead of turning it into heat, which is exactly what 12 V LED strips do: each segment is three LEDs and one resistor.
Other supplies: 3.3 V · 5 V · 9 V · 24 V. The method and edge cases are explained in the LED resistor guide, and wattage in resistor power ratings.
FAQ
What resistor do I need for an LED on 12 V?
For a red LED (≈2 V) at 20 mA: (12 − 2) ÷ 0.02 = 500 Ω, so use 510 Ω. For a blue or white LED (≈3.2 V) at 20 mA: 440 Ω, so 470 Ω. At 10 mA a red LED needs 1 kΩ.
What wattage resistor for an LED on 12 V?
A red LED at 20 mA puts 200 mW into a 510 Ω resistor, so use 1/2 W or larger (twice the dissipated power).
How many LEDs can I run in series on 12 V?
Leaving at least 1 V for the resistor: 5 × red / orange, 5 × yellow, 5 × green (traditional), 3 × true green, 3 × blue / white.
What resistor for a 12 V LED in a car?
Size it for 14.4 V, the charging voltage. For one red LED at 20 mA: (14.4 − 2) ÷ 0.02 = 620 Ω, rated 1/2 W. For one white LED: (14.4 − 3.2) ÷ 0.02 = 560 Ω, 1/2 W.