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Electronics & Hardware Engineering

LED Resistor Calculator — Series Resistance for Safe Current

R = (Vsupply − Vled) ÷ Iled; power dissipated = I² × R.

Find the series resistor value for a given supply voltage and LED forward voltage. Planning estimates only — verify with production tools and vendor pricing where applicable.

Inputs

148
14
150

Smart analysis

Recommendations

Tailored to your live inputs and result—guidance only, not professional advice.

  • Interpret

    Treat this as a planning estimate

    Primary result: Resistor value = 150 Ω. Re-run with optimistic and pessimistic inputs to understand the range—not just a single point.

Scenario studio

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Scenario A

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Scenario B

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Plain-English guide

Terms & how it works

Confused by a field? Read the short definitions here while you use the tool.

  • Supply voltage (V)

    The “Supply voltage (V)” value used in this tool’s formula. Adjust it to see results update live.

  • LED forward voltage (V)

    The “LED forward voltage (V)” value used in this tool’s formula. Adjust it to see results update live.

  • LED current (mA)

    The “LED current (mA)” value used in this tool’s formula. Adjust it to see results update live.

How this calculator works

Find the series resistor value for a given supply voltage and LED forward voltage. Planning estimates only — verify with production tools and vendor pricing where applicable. R = (Vsupply − Vled) ÷ Iled; power dissipated = I² × R. Example: 5 V supply, 2 V LED, 20 mA → 150 Ω resistor, 60 mW.

R = (Vsupply − Vled) ÷ Iled; power dissipated = I² × R.

Example: 5 V supply, 2 V LED, 20 mA → 150 Ω resistor, 60 mW.

When to use this LED Resistance

Common use cases

  • Find the series resistor value for a given supply voltage and LED forward voltage.
  • Sanity-check with this case: 5 V supply, 2 V LED, 20 mA → 150 Ω resistor, 60 mW.
  • The relationship is: R = (Vsupply − Vled) ÷ Iled; power dissipated = I² × R.

Localized examples

  • Electronics & Hardware Engineering: the example on this page uses the same formula as the widget.

What you get

  • Fields: Supply voltage (V), LED forward voltage (V), LED current (mA)
  • R = (Vsupply − Vled) ÷ Iled; power dissipated = I² × R.
  • Example on the page: 5 V supply, 2 V LED, 20 mA → 150 Ω resistor, 60 mW.

How to Calculate LED Resistance Step-by-Step

  1. 1Enter Supply voltage (V), LED forward voltage (V), LED current (mA). Use the values you have, not a catalog average, unless that is all you know.
  2. 2R = (Vsupply − Vled) ÷ Iled; power dissipated = I² × R.
  3. 3Worked case: 5 V supply, 2 V LED, 20 mA → 150 Ω resistor, 60 mW.
  4. 4Compare the result to last month’s invoice or a vendor calculator before you commit capacity.

Governing formula

R = (Vsupply − Vled) ÷ Iled; power dissipated = I² × R.

5 V supply, 2 V LED, 20 mA → 150 Ω resistor, 60 mW.

Example: set Supply voltage (V) = 5, LED forward voltage (V) = 2, LED current (mA) = 20, then read the result.

Variable definitions

  • supplyVoltage

    Supply voltage (V)

    The “Supply voltage (V)” field. Default 5; typical range 1–48.

  • ledForwardV

    LED forward voltage (V)

    The “LED forward voltage (V)” field. Default 2; typical range 1–4.

  • ledCurrentMa

    LED current (mA)

    The “LED current (mA)” field. Default 20; typical range 1–50.

  • Closed-form math (R = (Vsupply − Vled) ÷ Iled; power dissipated = I² × R.) misses idle time, egress, packet loss, and reserved capacity on the real bill.
  • Nothing here is uploaded for the calculation itself.

Frequently Asked Questions

R = (Vsupply − Vled) ÷ Iled; power dissipated = I² × R.

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Reviews & Ratings

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4.8

out of 5.0

4 reviews

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Your rating

Aisha K.

Mar 12, 2026

Clean layout and the results update instantly. Exactly what I needed for a quick planning check.

Daniel R.

Feb 28, 2026

Very usable on mobile. Would love a save/export option later, but the math feels solid.

Priya S.

Feb 3, 2026

The FAQ section answered my questions before I even had to search. Smooth dark mode too.

Marcus L.

Jan 19, 2026

Simple inputs, clear outputs. This replaced three bookmarks I used to juggle.

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