LED Resistor Calculator
Calculate the current-limiting resistor needed for an LED from the supply voltage, LED forward voltage and desired current (R = (Vs − Vf) / I).
- Resistor power dissipation
- 60.0 mW
Formula: R = (Vs − Vf) / I
About LED Resistor Calculator
LED Resistor Calculator is a free online calculator that gives you an instant, accurate result as you type. Calculate the current-limiting resistor needed for an LED from the supply voltage, LED forward voltage and desired current (R = (Vs − Vf) / I).
The calculation uses the standard formula R = (Vs − Vf) / I and updates live with every change to the inputs. Everything runs client-side in your browser — fast, private, and free to use as often as you like.
Typical LED forward voltages: red ≈ 1.8-2.2 V, green ≈ 2.0-3.0 V, blue and white ≈ 3.0-3.4 V, with 20 mA as a common operating current.
Frequently Asked Questions
Is LED Resistor Calculator free to use?
Yes. LED Resistor Calculator is completely free, with no sign-up, no downloads, and no usage limits. You can use it as many times as you like on any device with a web browser.
How accurate is this calculator?
The calculator applies the standard formula (R = (Vs − Vf) / I) with full floating-point precision and rounds only the displayed result. For most practical purposes the results are exact.
What resistor value should I actually buy?
Round up to the next standard E12 value (e.g. a calculated 150 Ω → use 150 Ω; a calculated 130 Ω → use 150 Ω) so the LED runs slightly dimmer but safe.
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