Calculator Inputs and Outputs
Inputs
- Supply voltage (V) — example: 12
- LED forward voltage (V) — example: 2.2
- Desired LED current (mA) — example: 20
Results
- Required series resistance (Ω)
- Resistor power dissipation (W)
- Recommended minimum resistor rating (W)
Formula used
Series resistor R = (Vs − Vf)/I; resistor power = I²R.
How to Use the LED Resistor Calculator
Enter the requested values, check the units and assumptions, then select Calculate LED Resistor. The built-in defaults provide a complete working example.
Formula
Series resistor R = (Vs − Vf)/I; resistor power = I²R.
Understanding the Results
The primary answer appears first. Supporting outputs show related quantities, conversions, dates, costs, ratios, or intermediate values. Calculations keep additional precision before display rounding.
Accuracy Tips
- Use measured values and consistent units.
- Review assumptions, rates, timing, and efficiency inputs.
- Recalculate after changing any condition.
Important Note
This tool provides an informational estimate. Confirm critical financial, medical, construction, scientific, tax, legal, or safety decisions with an appropriately qualified professional.
Calculation Standards
This tool uses documented formulas and high-precision internal values. Displayed results may be rounded for readability. Review the assumptions and verify important decisions with a qualified professional.
Read our calculation methodology