LED Calculator
LED Resistor Calculator
Find the correct current-limiting resistor for any LED. Works with Arduino (5V), ESP32 (3.3V), 9V, 12V, and any supply voltage. Recommends standard E12 resistor values and wattage rating.
Quick Colour Presets
Tap a colour to auto-fill the forward voltage, then adjust as needed.
Enter Values
All three fields are needed for the calculation.
Volts — e.g. 3.3, 5, 9, 12
Volts (Vf) — check datasheet
milliamps (mA) — typical: 10–20 mA
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Nearest standard E12 resistor value shown
Formula & Worked Example
Formula:
R = (V_supply − V_forward) / I_LED
P = (V_supply − V_forward) × I_LED
Example — White LED on 5V Arduino:
V_supply = 5V V_forward = 3.3V I = 20mA
R = (5 − 3.3) / 0.02 = 1.7 / 0.02 = 85 Ω → use 82 Ω (E12)
P = 1.7 × 0.02 = 0.034W → ¼W resistor is fine
Example — Red LED on 12V:
V_forward = 1.8V I = 20mA
R = (12 − 1.8) / 0.02 = 10.2 / 0.02 = 510 Ω → use 470 Ω (E12)
P = 10.2 × 0.02 = 0.204W → use ¼W resistor
R = (V_supply − V_forward) / I_LED
P = (V_supply − V_forward) × I_LED
Example — White LED on 5V Arduino:
V_supply = 5V V_forward = 3.3V I = 20mA
R = (5 − 3.3) / 0.02 = 1.7 / 0.02 = 85 Ω → use 82 Ω (E12)
P = 1.7 × 0.02 = 0.034W → ¼W resistor is fine
Example — Red LED on 12V:
V_forward = 1.8V I = 20mA
R = (12 − 1.8) / 0.02 = 10.2 / 0.02 = 510 Ω → use 470 Ω (E12)
P = 10.2 × 0.02 = 0.204W → use ¼W resistor
LED Forward Voltages Reference
Typical forward voltages by colour:
Infrared (IR): 1.2 – 1.8 V
Red: 1.6 – 2.0 V
Orange: 2.0 – 2.2 V
Yellow: 2.0 – 2.2 V
Green: 2.0 – 3.5 V
Blue: 2.5 – 3.5 V
White: 3.0 – 3.5 V
UV: 3.1 – 4.4 V
Always check your LED datasheet — values vary by manufacturer.
Infrared (IR): 1.2 – 1.8 V
Red: 1.6 – 2.0 V
Orange: 2.0 – 2.2 V
Yellow: 2.0 – 2.2 V
Green: 2.0 – 3.5 V
Blue: 2.5 – 3.5 V
White: 3.0 – 3.5 V
UV: 3.1 – 4.4 V
Always check your LED datasheet — values vary by manufacturer.