PreBuild Engineering
PCB calculators / Circuit design
Free tool · PreBuild Engineering

LED series resistor calculator

Pick the right current-limiting resistor and package size for an indicator or lighting LED.

Inputs

V
V
Red ≈ 1.8–2.2 V, green/blue/white ≈ 2.8–3.4 V
mA

Result

—

Why it matters

Too little resistance burns LEDs or overloads GPIO pins; too much leaves them dim. The resistor also needs a package rated for its power.

Formula

R = (Vsupply − n · Vf) / I_LED P = I² · R

Design tips

  • Check the GPIO pin's current limit if the MCU drives the LED directly.
  • Size the resistor package at least 2× the dissipated power.

More free calculators

Voltage divider (E24/E96)Best E24/E96 resistor pair, error and worst-case output. I²C pull-up resistorValid pull-up range from bus speed and capacitance. Crystal load capacitorsC1/C2 values from crystal load capacitance and stray. RC low-pass filterCutoff, time constant, settling and attenuation. Trace widthMinimum width for a current, copper weight and temperature rise. Trace resistance & voltage dropResistance, IR drop and power loss of a copper trace.

Results are engineering estimates from standard formulas and published approximations. Always confirm against component datasheets, your fabricator's capabilities and, for critical designs, simulation or measurement.