LED resistor calculator

Work out the series resistor for LEDs on a DC supply: one LED, several in series, or several identical strings in parallel (one resistor per string). For DC only; never use it for AC mains.

Supply voltage (V)LED voltage (V)LED current (mA)LEDs in series

Resistor per string: 440 Ω
Next standard value up: 470 Ω E12 · 470 Ω E24
Resistor power: 0.176 W
Resistor rated at least: 1/2 W

Formula: R = (supply voltage − LEDs in series × LED voltage) / current. Resistor power: P = current × (supply voltage − LEDs in series × LED voltage). Choose the next standard value up and a resistor rated at least twice that power.

Worked examples

Circuit	Resistor	Resistor power
5 V, 1 × red 2.0 V, 20 mA	Resistor150 Ω → 150 Ω	Resistor power0.06 W
5 V, 1 × white 3.2 V, 20 mA	Resistor90 Ω → 100 Ω	Resistor power0.036 W
12 V, 1 × white 3.2 V, 20 mA	Resistor440 Ω → 470 Ω	Resistor power0.176 W
12 V, 3 × white 3.2 V, 20 mA	Resistor120 Ω → 120 Ω	Resistor power0.048 W
12 V, 5 × red 2.0 V, 20 mA	Resistor100 Ω → 100 Ω	Resistor power0.04 W
24 V, 6 × white 3.2 V, 20 mA	Resistor240 Ω → 270 Ω	Resistor power0.096 W

Typical LED voltages: 1.9–2.3 V for red and yellow, 3.0–3.4 V for white, blue and green. Ours are on each family page: 5mm LEDs, 3mm LEDs, SMD LEDs.

Written with AI help from the specifications in our earlier catalog. Checked 11 October 2026.