LED Circuit Calculator

Resistor value from LED specs and supply voltage.

Supply Voltage (V)

LED Forward Voltage (V)

LED Forward Current (mA)

LEDs in Series

Tab to move between fields

Exact Resistor (Ω)

150

Nearest E24 Resistor (Ω)

150

Actual Current (mA)20

Resistor Power (mW)60

Min Resistor Rating (W)0.13

LED Power (mW)40

Total Circuit Power (mW)100

Resistor Voltage Drop (V)3

How to Use This Calculator

Enter your supply voltage (V) and the LED forward voltage (V) from the datasheet.
Set the desired LED forward current (mA) and the number of LEDs wired in series.
Review the calculated resistor value (Ω), nearest E24 standard resistor, and actual resulting current.
Check resistor power dissipation (mW) and minimum wattage rating to ensure safe operation.

How the result changes with Supply Voltage (V)

Supply Voltage (V): DC supply voltage powering the circuit.
LED Forward Voltage (V): Forward voltage drop across the LED (check datasheet; typical red ~2V, blue/white ~3.2V).
LED Forward Current (mA): Desired operating current through the LED in milliamps (typical 5mm LED: 20mA).
LEDs in Series: Number of LEDs connected in series.

Exact Resistor (Ω): Calculated resistor value using R = (Vs - Vf) / If.
Nearest E24 Resistor (Ω): Nearest standard E24 series resistor value (rounded up to protect LED).
Actual Current (mA): Actual current with the nearest standard resistor.
Resistor Power (mW): Power dissipated in the resistor.
Min Resistor Rating (W): Minimum wattage rating for the resistor (use at least 2x for safety margin).
LED Power (mW): Power consumed by the LED(s).
Total Circuit Power (mW): Total power drawn from the supply.
Resistor Voltage Drop (V): Voltage dropped across the current-limiting resistor.

Identify Input Parameters
4 parameters
Supply Voltage (V) = 5, LED Forward Voltage (V) = 2, LED Forward Current (mA) = 20, LEDs in Series = 1 = 4 input(s) provided
Calculate Exact Resistor
150 = 150
Calculate Nearest E24 Resistor
Nearest E24 Resistor
150 = 150
Calculate Actual Current
Actual Current = nearestResistor > 0
20 = 20
Calculate Resistor Power
Resistor Power = resistorOhms > 0
60 = 60