LED Resistor Calculator
Size the current-limiting resistor an LED needs, with the power rating it must carry.
An LED without a resistor destroys itself
Above its forward voltage an LED has almost no internal resistance, so current climbs steeply for a tiny voltage rise and the junction fails within seconds. The resistor is what sets the current. Typical forward voltages: red 1.8–2.2 V, green 2.0–3.0 V, blue and white 3.0–3.4 V.
What this page needs from you
This page asks for supply voltage in V, led forward voltage in V, led current in mA and leds in series. From those it returns resistor needed in Ω, together with voltage across the resistor, power in the resistor, recommended resistor rating and maximum leds in series. Every figure updates as you type, and nothing you enter leaves your browser.
Check the power rating, not just the value
Choosing a component by its resistance or capacitance alone leaves out the rating that actually determines whether it survives. Work out the power the part will dissipate and pick something rated for at least twice it: a resistor run at its limit gets hot enough to drift out of tolerance and to discolour the board.
The formula
R = (V_supply − V_forward × n) / I
Every result on this page comes from this formula. Nothing is rounded until the final display, so figures match a spreadsheet to the cent.
How to use the LED Resistor Calculator
- Fill in each field with your own figures — the defaults are only there as an example.
- The result updates as you type, so there is no button to press.
- Check the breakdown under the main result for the supporting numbers.
- Use the copy button to take the result with you, or share the link to reload the same inputs.
LED Resistor Calculator — frequently asked questions
Is this led resistor calculator free to use?
Yes. Every calculator on the site is free, needs no sign-up, and runs entirely in your browser, so your figures never leave your device.
How accurate is the result?
The maths is exact for the formula shown on the page. Accuracy in the real world depends on your inputs and on assumptions the formula cannot see, so treat the output as a well-grounded estimate rather than a quote.
Can I use it on my phone?
Yes. The page is responsive, weighs a few kilobytes and works offline once loaded, so it behaves the same on a phone as on a desktop.
What people search for
This page answers each of these searches. They are the exact phrases visitors use to find the led resistor calculator.
- led resistor calculator
- led dropping resistor
- what resistor for an led
- led series resistor
- current limiting resistor
About this calculator
Written and reviewed by The Samsung Calculator editorial team. Every calculator is written against a published formula, reviewed against at least one independent reference implementation, and dated when it changes.
Last reviewed September 14, 2026 · Calculation runs client-side · No data collected · Report an error