LED Resistor Calculator
Computes R = (Vs − n·Vf) / I, rounds up to E24, and estimates resistor wattage.
Limitation: Educational estimate only.
How to Use the LED Resistor Calculator
Enter the fields below, then review the educational estimate.
Enter supply voltage.
Derate power
The worksheet suggests roughly 2× calculated resistor power (minimum ¼ W) as a starting derating habit.
What This Calculator Estimates
Classic series current-limiting resistor design for indicator LEDs and simple DIY lighting experiments.
Worked Examples
5 V supply, 2 V LED, 20 mA
Inputs
Result
R = (5−2)/0.02 = 150 Ω.
Safety first
De-energize circuits before measuring. When in doubt, stop and consult a licensed electrician.
Frequently Asked Questions
Still have questions about this calculation?
Try the CalculatorFormulas & Assumptions
Transparent educational arithmetic. Not NEC design software or a wiring permit.
Formula
Resistance
R = (Vs − n · Vf) / I
Power
P = I² · R
Scientific Background
LED Vf varies with color and current. Parallel LED strings each need their own resistor; this tool models a single series string.
Sources & review
LED Resistor Calculator documents the references behind its formulas and assumptions. Always treat results as educational estimates, not personalized professional advice.
Last reviewed
July 22, 2026
Reference
physics.nist.gov
https://physics.nist.gov/cuu/Constants/index.htmlReference
nist.gov
https://www.nist.gov/pml/owm/wire-gauge-and-current-carrying-capacityFree Calculator Hub methodology
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