LED Series Resistor Calculator

Resistor Value for LED Current Limiting

Input Fields

Supply voltage

Vs

V

Voltage from power supply

LED forward voltage

Vf

V

Typical forward voltage of the LED

LED current

I

A

Desired current through LED (e.g., 0.02 A = 20 mA)

CalculateReset

Calculate automaticallyIf enabled, the result will update automatically when you change any value.

Your Results

Resistor Value

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LED Resistor Calculation Formula

$$R = \frac{V_{\text{supply}} – V_f}{I}$$

Where:

• $$R$$ = series resistor value (Ω)
• $$V_{supply}$$ = supply voltage (V)
• $$V_f$$ = forward voltage of LED (V)
• $$I$$ = desired current through LED (A)

This formula calculates the resistance needed to safely power an LED by dropping excess voltage from the supply.

KVA to Amps – Calculation Example

Given:

• $$V_{supply}$$ = 9 V
• $$V_f$$ = 2 V
• $$I$$ = 0.02 A (20 mA)

Calculation:

1. $$R = \frac{9 – 2}{0.02} = \frac{7}{0.02} = 350~\Omega$$

Using the correct resistor in series with an LED is crucial to prevent it from burning out due to excessive current. This calculator allows users to quickly input supply voltage, LED forward voltage, and desired current to find the appropriate resistor. It’s commonly used in breadboard prototyping, microcontroller projects, and embedded systems. The result should be rounded up to the nearest standard resistor value for practical use.