LED Resistor Calculator
Calculate the correct current-limiting resistor for an LED circuit to prevent burnout.
V
V
mA
Required Resistance
150.0 Ω
Resistor Power Dissipation60.0 mW
Required Resistance vs Supply Voltage
How to Size a Resistor for an LED
An LED needs a series resistor to limit current.
Formula
R = (V_supply - V_led) / I_led
Where:
Power dissipated in the resistor is P = (V_supply - V_led) x I_led.
Example Calculation
Drive a red LED (2.0 V forward) at 20 mA from a 5 V supply.
- 01Voltage across resistor = 5 - 2.0 = 3.0 V
- 02Current in amps = 20 / 1000 = 0.02 A
- 03R = 3.0 / 0.02 = 150 ohms
- 04Power = 3.0 x 0.02 = 0.06 W = 60 mW
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Ohm's Law Guide
A complete guide to Ohm's Law. Learn the relationship between voltage, current, and resistance, with practical examples, the power triangle, and circuit analysis tips.