LED Resistor Calculator
Every LED needs a resistor in series to limit the current through it. The formula is R = (Vs - Vf) / I: supply voltage minus the LED's forward voltage, divided by the current you want. A lower resistance gives more current and a brighter LED; a higher one is easier on the LED.
Enter your three values to get the nearest standard E24 resistor values in both directions, the current each one really gives, the power it wastes as heat, and the power rating to buy.
Result
R = (Vs - Vf) / I = (5 V - 2 V) / 0.02 A = 150 Ω
| Quantity | Exact E24 value |
|---|---|
| Resistor | 150 Ω |
| Actual current | 20 mA |
| Power dissipation | 0.06 W |
| Recommended power rating | 0.25 W |
E24 is the standard 5% resistor series: every value shown is a part you can buy anywhere. The recommended power rating carries at least twice the dissipation, so the resistor runs cool. With 5% tolerance parts the real current lands within a few percent of the figure shown.