LED resistor for 24 V
Resistor values for LEDs on 24 V industrial control, PLC indicators, trucks and 24 V LED strips. 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 24 V — change the LED or current to suit your part.
24 V LED resistor table at 20 mA
20 mA is the classic rating for 3 mm and 5 mm indicator LEDs. Formula: R = (24 − Vf) ÷ 0.020.
| LED color | Vf | Exact | E12 (up) | E24 (up) | Actual current | Power → rating |
|---|---|---|---|---|---|---|
| Red / orange | 2 V | 1.1 kΩ | 1.2 kΩ | 1.1 kΩ | 20 mA | 440 mW → 1 W |
| Yellow | 2.1 V | 1.1 kΩ | 1.2 kΩ | 1.1 kΩ | 19.9 mA | 440 mW → 1 W |
| Green (traditional) | 2.2 V | 1.09 kΩ | 1.2 kΩ | 1.1 kΩ | 19.8 mA | 430 mW → 1 W |
| True green | 3 V | 1.05 kΩ | 1.2 kΩ | 1.1 kΩ | 19.1 mA | 400 mW → 1 W |
| Blue / white | 3.2 V | 1.04 kΩ | 1.2 kΩ | 1.1 kΩ | 18.9 mA | 390 mW → 1 W |
24 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 | 2.2 kΩ | 2.2 kΩ | 2.2 kΩ | 10 mA | 220 mW → 1/2 W |
| Yellow | 2.1 V | 2.19 kΩ | 2.2 kΩ | 2.2 kΩ | 9.95 mA | 220 mW → 1/2 W |
| Green (traditional) | 2.2 V | 2.18 kΩ | 2.2 kΩ | 2.2 kΩ | 9.91 mA | 220 mW → 1/2 W |
| True green | 3 V | 2.1 kΩ | 2.2 kΩ | 2.2 kΩ | 9.55 mA | 200 mW → 1/2 W |
| Blue / white | 3.2 V | 2.08 kΩ | 2.2 kΩ | 2.2 kΩ | 9.45 mA | 200 mW → 1/2 W |
LEDs in series on 24 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 | 11 | 22 V | 100 Ω (40 mW) | 92% |
| Yellow | 10 | 21 V | 150 Ω (60 mW) | 88% |
| Green (traditional) | 10 | 22 V | 100 Ω (40 mW) | 92% |
| True green | 7 | 21 V | 150 Ω (60 mW) | 88% |
| Blue / white | 7 | 22.4 V | 82 Ω (31 mW) | 93% |
When the supply is not exactly 24 V
Current with the 20 mA resistor from the table above (1.1 kΩ for red, 1.1 kΩ for white) at the voltages this supply really sees:
| Condition | Supply | Red LED | White LED |
|---|---|---|---|
| Lower PLC tolerance (−15%) | 20.4 V | 16.7 mA | 15.6 mA |
| Nominal | 24 V | 20 mA | 18.9 mA |
| Truck alternator charging | 28.8 V | 24.4 mA | 23.3 mA |
Notes for 24 V circuits
At 24 V a single indicator LED wastes over 90% of the power in its resistor, and at 20 mA that is close to half a watt — the table recommends a 1 W part, which is physically large and runs warm. Industrial indicators therefore either run at a few milliamps (at 5 mA a red LED needs 4.7 kΩ — 4.4 kΩ rounded up — and dissipates only about 0.1 W) or use a constant-current diode. In trucks and buses, a 24 V system charges at about 28–29 V, so size the resistor for the higher voltage.
The better answer at 24 V is long series strings: up to eleven red LEDs (22 V) or seven white LEDs (22.4 V) still leave 1 V for the resistor, and a string of six white LEDs (19.2 V) leaves a comfortable 4.8 V so the current barely changes when the supply does. 24 V LED strips use the same trick, with several LEDs sharing each resistor.
Other supplies: 3.3 V · 5 V · 9 V · 12 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 24 V?
For a red LED (≈2 V) at 20 mA: (24 − 2) ÷ 0.02 = 1.1 kΩ, so use 1.1 kΩ. For a blue or white LED (≈3.2 V) at 20 mA: 1.04 kΩ, so 1.1 kΩ. At 10 mA a red LED needs 2.2 kΩ.
What wattage resistor for an LED on 24 V?
A red LED at 20 mA puts 440 mW into a 1.1 kΩ resistor, so use 1 W or larger (twice the dissipated power).
How many LEDs can I run in series on 24 V?
Leaving at least 1 V for the resistor: 11 × red / orange, 10 × yellow, 10 × green (traditional), 7 × true green, 7 × blue / white.
Can I use a 12 V LED on 24 V?
Not directly. A "12 V" LED already contains a resistor sized for 12 V; on 24 V it would draw far more current. Add a series resistor equal to roughly 12 V divided by its rated current, or put two identical 12 V LEDs in series.