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.
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 | 150 Ω → 150 Ω | 0.06 W |
| 5 V, 1 × white 3.2 V, 20 mA | 90 Ω → 100 Ω | 0.036 W |
| 12 V, 1 × white 3.2 V, 20 mA | 440 Ω → 470 Ω | 0.176 W |
| 12 V, 3 × white 3.2 V, 20 mA | 120 Ω → 120 Ω | 0.048 W |
| 12 V, 5 × red 2.0 V, 20 mA | 100 Ω → 100 Ω | 0.04 W |
| 24 V, 6 × white 3.2 V, 20 mA | 240 Ω → 270 Ω | 0.096 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.