LED Resistor Calculator
Free calculate the current-limiting resistor value for led circuits. Get instant, accurate results with our easy-to-use calculator.
Input Parameters
Typical: Red 1.6-2.2V, Green 1.9-3.2V, Blue 2.9-3.7V, White 3.0-3.4V
Typical: 5-30 mA for standard LEDs, 100+ mA for high-power LEDs
Results
Enter parameters to calculate
What is an LED Resistor?
An LED resistor (current-limiting resistor) is a resistor placed in series with an LED to limit the current flowing through it. LEDs require a specific forward voltage and current to operate properly, and without a resistor, they can be damaged by excessive current.
The resistor value is calculated using Ohm's Law: R = (V_s - V_f) / I_f, where V_s is the supply voltage, V_f is the LED's forward voltage drop, and I_f is the desired forward current.
Different LED colors have different forward voltages due to the semiconductor materials used. Always check the LED datasheet for exact specifications, and choose a resistor with appropriate power rating to handle the power dissipation.
LED Resistor Formula
Where:
- • R = Resistor value (Ω)
- • V_s = Supply voltage (V)
- • V_f = LED forward voltage (V)
- • I_f = Desired forward current (A)
Power dissipation in resistor:
P = (V_s - V_f) × I_f
Choose a resistor with power rating at least 2× the calculated power.
How to Calculate
-
1
Determine supply voltage
This is the voltage of your power source (battery, power supply, etc.).
-
2
Find LED forward voltage
Check the LED datasheet or use typical values: Red ~2V, Green ~2.5V, Blue/White ~3.3V.
-
3
Choose desired current
Typical values: 5-30 mA for standard LEDs. Convert mA to A (divide by 1000).
-
4
Calculate resistor value
R = (V_s - V_f) / I_f. Round up to nearest standard resistor value.
Practical Examples
Example 1: Red LED with 9V Battery
Supply: 9V, Red LED (V_f = 2V), Desired current: 20 mA.
Solution:
R = (9V - 2V) / 0.02A = 7V / 0.02A
R = 350 Ω (use 360 Ω standard value)
Power: P = 7V × 0.02A = 0.14W (use 0.25W resistor)
Example 2: White LED with 12V Supply
Supply: 12V, White LED (V_f = 3.2V), Desired current: 30 mA.
Solution:
R = (12V - 3.2V) / 0.03A = 8.8V / 0.03A
R = 293 Ω (use 300 Ω standard value)
Applications
Indicator Lights
Power indicators, status lights, and visual feedback in electronic devices and appliances.
Displays
Seven-segment displays, dot matrix displays, and LED arrays for information display.
Lighting
Decorative lighting, accent lighting, and low-power illumination applications.
Education
Teaching basic electronics, circuit design, and Ohm's Law in educational projects.
Frequently Asked Questions
Why do LEDs need a resistor?
LEDs have very low resistance and will draw excessive current if connected directly to a voltage source, causing them to burn out. The resistor limits current to safe levels.
What if my calculated resistor value isn't standard?
Round up to the nearest standard E12 or E24 resistor value. It's better to have slightly less current than too much. Common values: 220Ω, 330Ω, 470Ω, 680Ω, 1kΩ, etc.
Can I connect multiple LEDs in series?
Yes! For N LEDs in series: R = (V_s - N×V_f) / I_f. Make sure V_s > N×V_f. All LEDs will have the same current.
What power rating should the resistor have?
Calculate power: P = (V_s - V_f) × I_f. Use a resistor with at least 2× this power rating for safety. Common: 0.25W (1/4W), 0.5W (1/2W), 1W.
What happens if I use the wrong resistor value?
Too small: LED may burn out from excessive current. Too large: LED will be dim or not light up. Always calculate and verify before connecting!