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Electronics / LOCAL TOOL

LED Resistor Calculator

Choose the next preferred LED current-limiting resistor and inspect branch power.

Runs locally — input is never uploaded
LED branchOne resistor per parallel branch
Preferred resistor series
1 LED and 1 resistor in one branch

A plain current is amperes: enter 12 mA, not 12, for twelve milliamps. E12 is a subset of E24, so their recommendation can match.

ResultReady when you are
R=Vs−NVfIP=I2R

WHAT IT DOES

Choose a real preferred value, not an impossible ideal resistor.

Enter the supply, LED forward voltage, desired branch current, and series/parallel arrangement. The calculator moves upward to the next E12, E24, or E96 resistor, recalculates the actual current, and shows per-branch and whole-circuit dissipation.

Why use it?

Use it to estimate a current-limiting resistor for a stated LED arrangement and inspect the current after selecting a preferred resistor value.

How to use this tool

  1. Enter the supply, forward voltage per LED, desired branch current, LEDs in series, and parallel branch count.
  2. Choose the preferred-value series and calculate. Read the selected resistor and recalculated current, not only the ideal resistance.
  3. Check per-branch and total power. Each parallel branch needs its own resistor in this model; review the actual LED and resistor ratings before building the circuit.

Details and limitations

  • Every parallel LED branch is given its own resistor; sharing one resistor between unmatched parallel branches is not treated as equivalent.
  • The nominal power suggestion is the next common rating at least twice the calculated steady-state dissipation. That is a visible engineering margin, not a guarantee for a particular package or environment.
  • LED forward voltage is an operating-point estimate that moves with device, current, and junction temperature, so the actual part datasheet remains authoritative.

COMMON QUESTIONS

LED Resistor questions

Why does the selected resistor exceed the ideal value?
Selecting the next preferred value keeps the calculated branch current at or below the requested current under the stated nominal voltages.
Can parallel LEDs share one resistor?
This tool deliberately assumes one resistor per branch because forward-voltage differences can make parallel LEDs share current unevenly.
Is the suggested wattage automatically safe?
No. It provides a two-times steady-state margin. Check ambient derating, pulse energy, working voltage, enclosure temperature, and the actual resistor datasheet.