Ohm’s law and LED resistors
Solve low-voltage DC resistance, current and power, or size an ideal LED series resistor. Change the inputs to update the chart or diagram.
Your inputs
Values shown are editable examples; verify your own measurements and product specifications. Results update as you edit.
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How it works
- = × ; P = × ; Ideal series resistance = (Vs − × ) / ; Resistor dissipation = (Vs − × ) ×
- Worked example: 5 V / 250 Ω = 0.02 A; (5 − 2) V / 0.02 A = 150 Ω; 0.06 W × 2 = 0.12 W
Input and formula key
Your result
Complete the inputs to see your result.
Assumptions and limitations
Voltage is limited to 0–60 V DC; this is a model limit, not a safety rating. Ohm’s law applies to the resistor, not the nonlinear LED. LED mode uses identical LEDs in one series string and your datasheet forward voltage at the target current. Supply must exceed combined LED drops. Results are ideal values, not automatically selected standard resistor sizes. The power multiplier is user-entered. Excludes AC, parallel LED strings, tolerances, heat design and real component ratings.
Sources
- Adafruit — LEDs and series resistors Sources reviewed: 2026-10-09
