LED resistor calculator
An LED needs a series resistor to set its current — without one it draws whatever the supply allows and burns out. The resistor drops the difference between the supply and the LED's forward voltage.
Results
- Exact resistance
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- Nearest E12 value
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- Current with E12 part
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- Resistor power
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Results update as you type.
Formula
R = (Vsupply − Vf) / If
P = (Vsupply − Vf) × If
How it works
Typical forward voltages: red ≈ 1.8–2.2 V, green/yellow ≈ 2.0–2.4 V, blue/white ≈ 3.0–3.4 V. Read it from the datasheet where you can; the value matters most at low supply voltages.
The exact resistance rarely matches a stock part, so the nearest E12 value is shown too. Picking the next value up nudges the current slightly below target, which is the safe direction.
The power figure is what the resistor dissipates. Choose a resistor rated at roughly twice that to stay cool — a 1/4 W part is fine below about 125 mW.