For a standard 5mm red LED on a 5V logic supply, use a 220Ω, 1/4W resistor. For a 12V automotive circuit, use 470Ω. For 24V industrial panels, use 1kΩ. If you are wiring multiple LEDs in parallel, you must use one resistor per LED to prevent thermal runaway. The charts and decision trees below provide the exact E24-series values and wattage ratings for standard AlGaInP and InGaN semiconductor junctions.
The Master LED Resistor Chart (Standard 5mm & SMD)
The following table provides the nearest EIA E24 standard resistor values for common LED colors. The forward voltage (Vf) ranges are based on typical semiconductor physics for standard 20mA indicator LEDs. Always calculate your exact value using the formula: R = (Vs - Vf) / If, then round up to the nearest E24 value to protect the LED.
| LED Color / Type | Typical Vf (V) | Target If (mA) | Resistor @ 5V (Ω) | Resistor @ 12V (Ω) | Resistor @ 24V (Ω) |
|---|---|---|---|---|---|
| Red (AlGaInP) | 2.0 | 20 | 150Ω | 510Ω | 1.1kΩ |
| Yellow (AlGaInP) | 2.1 | 20 | 150Ω | 510Ω | 1.1kΩ |
| Green (InGaN) | 3.0 | 20 | 100Ω | 470Ω | 1.1kΩ |
| Blue (InGaN) | 3.2 | 20 | 91Ω | 470Ω | 1kΩ |
| White (InGaN) | 3.0 | 20 | 100Ω | 470Ω | 1.1kΩ |
| Infrared (IR) | 1.2 | 20 | 200Ω | 560Ω | 1.2kΩ |
| Ultraviolet (UV) | 3.3 | 20 | 91Ω | 430Ω | 1kΩ |
How to Read the Chart and Apply Derating
The most common mistake hobbyists make is sizing the resistor's wattage based on a 5V USB supply, then moving that same physical resistor to a 12V or 24V circuit. The resistance value (Ω) limits the current, but the wattage rating (W) dictates how much heat the physical package can survive.
A standard 1/4W (0.25W) carbon or metal film resistor is only rated for 0.25W at an ambient temperature of 70°C. If you are installing this inside an enclosed project box, an automotive dashboard, or an industrial control panel where ambient temperatures reach 85°C, the resistor derates by roughly 50%. Your safe maximum dissipation drops to 0.125W.
Worked Example (12V Blue LED):
- Supply (Vs): 12V
- LED Vf: 3.2V
- Current (I): 0.02A
- Voltage across resistor: 12V - 3.2V = 8.8V
- Power dissipated (P = V × I): 8.8V × 0.02A = 0.176W
Because 0.176W exceeds the 0.125W derated limit for a 1/4W resistor in a warm enclosure, a 1/4W resistor will overheat and drift in value or fail open. You must step up to a 1/2W physical package for this 12V circuit.
Decision Tree: Picking Your Exact Resistor
Use this decision path to terminate your component selection. Do not guess; follow the logic to your specific physical package and tolerance.
| Installation Condition | Calculation Rule | Concrete Pick (Value & Package) |
|---|---|---|
| 5V Logic (Arduino, ESP32, USB) | Calculate for 5.0V. Max power is ~0.06W. | Nearest E24 value, 1/4W, 5% tolerance. |
| 12V Automotive / Battery | Calculate for 14.4V (alternator charging voltage), not 12V. | Next highest E24 value, 1/2W package. |
| 24V Industrial (PLC, HVAC) | Calculate for 26V (tolerance margin). Expect high heat. | Next highest E24 value, 1W Metal Oxide. |
| Multiple LEDs in Parallel | Never share one resistor. Calculate per-LED. | Individual 1/4W resistors for each LED. |
| High-Power LEDs (1W, 3W, 5W) | Resistors will waste massive power as heat. | NO RESISTOR. Use a constant-current driver. |
What This Chart Cannot Tell You (Edge Cases)
Reference charts assume steady-state DC current and standard indicator LEDs. They fail to account for these three common real-world scenarios:
- PWM Dimming with Microcontrollers: If you are driving an LED with an ESP32 or Arduino using Pulse Width Modulation (PWM) for dimming, the average power drops, but the peak instantaneous power remains identical to a 100% duty cycle. You must still size the resistor's wattage for the full continuous current, or the rapid thermal cycling will crack the resistive element over time.
- Parallel Wiring Current Hogging: If you wire three blue LEDs in parallel with a single shared resistor, the LED with the lowest forward voltage (due to manufacturing tolerance) will draw the most current. As it heats up, its Vf drops further, drawing even more current until it burns out, shifting the burden to the next LED in a cascading failure. Always use one resistor per LED.
- Multiplexed LED Matrices: In 7-segment displays or LED matrices, the LEDs are only on for a fraction of the time (duty cycle). To maintain perceived brightness, the peak current during the 'on' pulse must be much higher than the 20mA continuous rating. Standard resistor charts will result in a dim display; you must calculate for the peak pulse current (often 50mA-100mA) as specified in the LED's 'Peak Forward Current' datasheet row.
Quick-Jump Bookmark Rows for Common Builds
Stop calculating and start building. Here are the exact, verified Bill of Materials (BOM) picks for the most common workbench and jobsite scenarios. These part numbers reference standard, widely available through-hole components from major distributors.
- Arduino Nano / ESP32 DevKit Status LED (5V):
Value: 220Ω | Wattage: 1/4W | Part Example: Yageo CFR-25JR-52-220R
Use this for standard GPIO pin indicators where you want maximum brightness without exceeding the 40mA absolute max pin limit. - 12V Motorcycle Dashboard Indicator:
Value: 470Ω | Wattage: 1/2W | Part Example: Vishay PR02000204700JR500
Sized for 14.4V alternator spikes. The 1/2W physical size handles the heat inside a sun-baked dash pod, and the metal film construction resists vibration better than carbon composition. - 24V Industrial PLC Cabinet Light:
Value: 1.2kΩ | Wattage: 1W | Part Example: Yageo FMP100JR-52-1K2
Industrial 24V lines can spike to 30V during inductive load switching. A 1W metal film or metal oxide resistor provides the thermal mass to absorb transient spikes without drifting out of tolerance. - 5V IR Blaster for TV Control (High Current):
Value: 10Ω | Wattage: 1/2W | Part Example: Stackpole CF12JT10R0
IR LEDs (like the TSAL6200) are often pulsed at 100mA for remote control range. Standard 1/4W resistors will burn up. Use a low-value, 1/2W resistor and drive it via a 2N2222 NPN transistor, not directly from a microcontroller GPIO.
For a deeper dive into LED physics and semiconductor junction behaviors, refer to the comprehensive LED guides on Adafruit. Always verify your specific LED's datasheet for its exact forward voltage, as modern high-efficiency LEDs can vary by up to 0.5V from the typical values listed in our master chart.
