LED Series Resistor Calculator
Estimate a series resistor and its dissipation for one LED branch.
Your inputs
Calculation results
Formula & assumptions
Resistance = (supply−forward voltage)/current; verify component ratings before use.
Values use the specified units. Calculations use floating-point arithmetic. Check input measurements and formula assumptions before applying the result.
Compare your scenarios
Save up to five results to compare changes side by side. Scenarios stay in this tab until you clear or reload it.
Using LED Series Resistor Calculator
Estimate a series resistor and its dissipation for one LED branch.
- Enter supply voltage, led forward voltage, target current using the units printed under each field.
- Choose Calculate, or enable live updates. Review the result labels and formula assumptions.
- Save scenarios to compare up to five variations, then copy the report or download JSON or CSV.
Example
Supply voltage: 5 volts LED forward voltage: 2 volts Target current: 20 milliamps Ideal resistance · ohms: 150 Resistor dissipation · watts: 0.06 LED power · watts: 0.04
Questions & answers
What does LED Series Resistor Calculator calculate?
Estimate a series resistor and its dissipation for one LED branch.
Which units should I enter?
Supply voltage uses volts. LED forward voltage uses volts. Target current uses milliamps. Convert values to these units before calculating.
Which formula does it use?
Resistance = (supply−forward voltage)/current; verify component ratings before use.
What does the included example show?
Supply voltage: 5 volts; LED forward voltage: 2 volts; Target current: 20 milliamps. Result: Ideal resistance · ohms = 150; Resistor dissipation · watts = 0.06; LED power · watts = 0.04.
Can I compare different settings?
Yes. Save a scenario, change the inputs and save another result. Up to five scenarios are compared in this tab; they disappear when you reload or leave.
Can I export the calculation?
Copy the JSON report or download JSON and CSV with inputs, result labels and numeric values. Processing uses local JavaScript; no calculation request is sent to our server. Displayed values use up to 10 significant digits; exports retain JavaScript numeric precision.
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