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Current Limiting Resistance Calculator for LED

LED Technical Information



LED Technical Information

The calculators on this page can be used to find current limiting resistors and currents for Light Emitting Diodes.

The first calculator determines the resistance for a desired LED current while the second calculates the current for a given resistance.

LED - Current and Resistance Calculator Diagram

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Supply Voltage

Voltage Drop Across LED

Desired LED Current

Calculated Limiting Resistor

Calculated Resistor Wattage


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Voltages in Volts - Current in Milliamps - Resistance in Ohms


When selecting resistors - It is advisable to choose the next higher standard value.


A browser capable of running Javascript is required for this calculator.

LEDs should always be connected in series or series-parallel for longer or larger arrays/clusters. We normally build them with 3 LEDs and one resistor that is sized to match the supply voltage or power source. For larger or longer clusters/arrays, connect one series to another in parallel. To determine the "Voltage Drop", multiply the LED's "Forward Voltage" as shown on the LED's data sheet by the number of LEDs to be installed.

The "Desired Current" is listed on the LED's data sheet as 20mA, You can go lower or higher by a few mA at a time to obtain the light volume and brightness level you seek. BUT, 20mA is the median that most will apply for max life and brightness.

Entering a zero for the LED voltage drop will yield the resistance and wattage for a resistance only circuit.