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LED Series Resistor Calculator — result sheet
Choose a current-limiting resistor for one or more LEDs in series and estimate the resistor voltage and power.
Inputs used
Results
Visual chart
Breakdown
Calculation steps
Returned data table
Formula and methodology
Formula: R = (Vsupply − N·Vforward) ÷ I − Rother; resistor power is P = I²R.
A series resistor absorbs the voltage left after the LED forward-voltage drops and limits current. This tool lets you include several identical LEDs in series and an additional switch or wiring resistance, then exposes the resistor power that a component must safely dissipate.
This result follows the calculator's declared inputs, precision, validation boundaries, and model limits.
Input contract
- Supply voltage — V; minimum 1.0E-6; maximum 10000
- Forward voltage per LED — V; minimum 1.0E-6; maximum 10000
- LEDs in series — LEDs; minimum 1.0E-6; maximum 1000
- Target LED current — mA; minimum 1.0E-6; maximum 1000000
- Other series resistance — Ω; minimum 0; maximum 1000000
Worked example
| Input | Value |
|---|---|
| Supply voltage | 5 |
| Forward voltage per LED | 2 |
| LEDs in series | 1 |
| Target LED current | 20 |
| Other series resistance | 0 |
A 5 V supply, 2 V LED, and 20 mA target current require about 150 Ω and dissipate about 0.06 W.
Assumptions and limits
- LED forward voltage is treated as a fixed value at the chosen operating current and temperature.
- The LEDs share the same series current and the supply is treated as a DC source without ripple or transient modeling.
- The result is a design starting point; select a resistor with an appropriate power rating and verify the actual LED current in the finished circuit.
Calculator note
Source and methodology
Use the official WorldCalculate methodology policy for the source, formula, precision, and boundary standards behind this calculator.
Planning estimate, not financial, medical, legal, or professional advice. © WorldCalculate — reuse with attribution. Built and curated by Hassan ALRowaie.
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