Science & engineering
LED series resistor calculator
Estimate the ideal resistor and dissipation for a low-voltage DC LED string.
A clear answer. Here’s how.
Uses the supplied forward-voltage estimate at your target current: R = (Vsupply − count × Vf)/I. Requires positive resistor voltage headroom. Reports ideal resistance, resistor dissipation and total LED electrical power. Does not choose a commercial resistor value, rating, thermal margin, tolerance, current-regulated driver or mains circuit.
See a worked example
Worked example
A fixed demonstration, separate from the values you enter above.
- DC supply (V)
- 5
- Forward voltage per LED at target current (V)
- 2
- LEDs in series
- 1
- Target string current (mA)
- 20
Example result
- Ideal series resistance
- 150 Ω
- Resistor voltage drop
- 3 V
- Resistor dissipation
- 0.06 W
- Total LED electrical power
- 0.04 W
- Supply electrical power
- 0.1 W
Ideal target value only. Choose actual values and ratings using the component specifications and operating conditions.