ABC Tools
LED Series Resistor Calculator illustration

LED Series Resistor Calculator

Computes the series resistor needed to run one or more LEDs from a given supply: exact value, the next standard E24 value, the resulting current and the power rating the resistor needs.

Read the full guide to this tool

Red ≈ 1.8–2.2 V, green/yellow ≈ 2–2.4 V, blue/white ≈ 3–3.4 V.
20 mA is the classic indicator-LED current.

Notes

  • R = (V_supply − n·V_forward) / I. The resistor absorbs whatever voltage the LEDs do not drop.
  • Pick a resistor power rating at least twice the computed dissipation so it stays cool.

Explore the idea

This interactive demo needs JavaScript.

Read the full guide for the explanation behind it

Related tools

Ohm's Law Calculator

Any two of V, I, R, P — get all four.

Resistor Color Code Calculator

4- and 5-band colors → value, or value → colors.

Active Filter Designer (Sallen-Key)

Butterworth, Chebyshev or Bessel — component values and Bode plot.

Antenna Radiation Pattern Explorer

Polar plots of dipoles, Yagis and phased pairs — see why more elements mean a narrower beam.

Capacitor Charge Calculator

RC time constant, charge curve and stored energy.

E-Series Resistor Solver

Best E12–E96 resistor or pair for any value or ratio.