LED Calculator
Compute LED current/resistor from supply, forward voltage and resistance.
Input Data
Vcc
Vf
Current
Results
Computed value.
150
Explanatory note.
限流電阻 R = (5−2)/0.02 = 150 Ω；建議選 ≥ 150 Ω（E12）。
At a glance:I = (V_cc − V_f)/R for an LED with series resistor. Complements led-resistor and ohm's-law.
Formula
I = (V_cc − V_f) / R.
How to Use
- Enter supply, V_f and resistor (or current).
- The tool returns the result.
Case Studies
V_cc=5, V_f=2, R=150
I ≈ 20 mA.
FAQ
V_f varies by color?
Red ~1.8 V, blue/white ~3.0–3.4 V.
Related Tools
References
Content review: Calculatorism Science Team. Results are for reference only; please refer to the relevant authorities for the official figures.