LED series resistor
Calculate, convert and check circuit values in your browser.
Inputs
Results
- Resistance
- 150 Ω
- Power loss
- 0.06 W
- Voltage drop
- 3 V
Formula and assumptions
R = (Vin − nVf) / I; P = I²R
Questions, examples and engineering limits
Calculate an LED series resistor from supply voltage, forward voltage, current and LED count. Check dissipated power and worst-case selection limits.
Content updated:
How is LED Series Resistor Calculator: Resistance and Power calculated?
Use R = (Vin−nVf)/I; P = I²R. Calculate an LED series resistor from supply voltage, forward voltage, current and LED count. Check dissipated power and worst-case selection limits.
Sources: ti.com [1]
How do I calculate this example: Vin = 5 V, Vf = 2 V, I = 20 mA, n = 1?
R = 150 Ω; P = 0.06 W. This is a calculated example under the model stated above; it is not a measured component specification.
Which units does LED Series Resistor Calculator: Resistance and Power use?
V, mA, Ω, W. Convert prefixes before substituting values; keep the input and output units attached to every number.
Sources: ti.com [1]
Does Ohm’s law apply to an LED directly?
An LED is nonlinear. Use its forward-voltage/current data; apply Ohm’s law to the series resistor, not a fixed LED resistance.
Sources: ti.com [1]
Is calculated power the resistor rating I should buy?
No. Choose a rating with margin for ambient temperature, pulses, tolerance and the manufacturer’s derating curve.
Sources: openstax.org [1]
Can parallel LEDs share one resistor?
Current may divide unevenly because forward voltages differ. Usually provide branch current limiting or a suitable constant-current driver.
Sources: e2echina.ti.com [1]
Answers use the stated model and units. Examples are calculated values, not measurements or component ratings.