LED resistor calculator
Interactive engineering and procurement calculator. Instant client-side computation with no sign-up.
Circuit values
Resistor
Required resistance
R = (Vsupply − Vf) ÷ I
150 Ω
Voltage dropped across R
Vsupply − Vf
3 V
Resistor power (P = I²·R)
Pick a resistor rated at ~2× this value
60 mW
Nearest E24 value: 150 Ω — actual LED current ≈ 20 mA (0% from target).
About the calc
A single resistor sets LED current to (Vsupply − Vf) ÷ R. Typical forward voltages: red ≈ 1.8–2.2 V, green ≈ 2.0–2.4 V, blue/white ≈ 3.0–3.4 V — use the datasheet value for the exact LED. Check your resistors against a multimeter; E24 values are close enough for an indicator but not for a precision brightness match.