ELECTRONICS · CALCULATOR

Resistor for LED calculator

Free resistor for LED calculator: get series resistor and resistor dissipation from supply voltage, led forward voltage, led current and leds in series.

Written by Chameera Sampath · Not yet reviewed by a licensed electrician. See the methodology.

US (NEC) only · NFPA 70 / NEC — locally adopted editionDefaults are US values. Verify the locally adopted NEC edition and project data.Official reference ↗

Project inputs

Measurements

Supply voltage

LED forward voltage

LED current

LEDs in series

Updates as inputs change. Unit changes preserve the same physical values.

THE MATH BEHIND THE ANSWER

Method & assumptions

R = (Vs − nVf) / I; P = I²R

Supply must exceed combined LED voltage. Select a standard resistor and appropriate power margin.

Results do not check every aspect of an electrical installation. The calculators follow US (NEC) practice only; a regional preset changes defaults such as voltage and units, and no result certifies NEC compliance.

Sources and validation →

Worked example

Supply voltage: 12 V · LED forward voltage: 2 V · LED current: 20 mA · LEDs in series: 1

Series resistor: 500 Ω · Resistor dissipation: 0.2 W

This example uses the stated inputs; results for the entered values appear above.

Explore the electronics branch →See the related electrical concepts →

Estimating and invoicing tool

Ampxa is developing an estimating and invoicing application for electrical contractors. The list below receives notice when it opens.