LED Resistor Calculator
Estimate an ideal series resistor and its dissipation for a DC LED string.
Choose the first nominal E12/E24 value at or above the ideal resistance. Tolerance is entered separately (0–20%); series membership does not establish a component’s tolerance. The range assumes fixed supply and LED forward voltage. No power-rating or thermal design is provided.
Values per decade (multiply by powers of 10 Ω)
E12: 10, 12, 15, 18, 22, 27, 33, 39, 47, 56, 68, 82
E24: 10, 11, 12, 13, 15, 16, 18, 20, 22, 24, 27, 30, 33, 36, 39, 43, 47, 51, 56, 62, 68, 75, 82, 91
R = (Vs − N Vf)/I; PR = I²R; I = mA/1000
Result
A QUICK WALKTHROUGH
How to use this tool
- Choose the mode and enter the values.
- Read the formula and limitations before interpreting the result.
Formula and limits
DC series estimate only: supply must exceed count × forward voltage. Voltage 0.000001–1000000000 V; current 0.000001–1000000000 mA; count integer 1–1000. The E12/E24 table and a separately entered resistor tolerance are used for nominal intervals. No resistor rating, thermal or safety assessment. R = (Vs − N Vf)/I; PR = I²R; I = mA/1000
GOOD TO KNOW
Common questions
Does this evaluate a real component or circuit?
No. This is a nominal calculation from the inputs, not component selection or a safety assessment.