💡 LED Resistor Calculator

🛡️ 100% Client‑Side — Private
Single · Series · Parallel — Power Rating & Color Code
V
V
mA
📊 Results Single LED
150 Ω
Standard value (E24): 150 Ω
Resistor Power
0.06 W
Recommended Rating
1/4 W
LED Current (actual)
20.0 mA
Voltage Drop (total)
2.0 V
✓ Real‑time · Ohm's Law · Standard E24 values

📘 LED Resistor Guide

LEDs are current-driven devices. Without a current-limiting resistor, an LED will draw excessive current and burn out. This calculator helps you determine the correct resistor value based on Ohm's Law: R = (Vs - Vf) / If.

❓ FAQ

Why do I need a resistor for an LED?

LEDs have very low internal resistance once forward voltage is reached. Without a resistor, current skyrockets and destroys the LED. The resistor limits current to a safe level.

Can I use one resistor for multiple parallel LEDs?

Not recommended. Due to manufacturing variations, LEDs have slightly different forward voltages, causing unequal current sharing. The LED with the lowest Vf will hog current and fail first, triggering a cascade failure. Use a separate resistor for each parallel LED.

Why round up to the next standard resistor value?

Rounding up (e.g., 165Ω → 220Ω) reduces current slightly, which extends LED lifespan with minimal brightness loss. Rounding down increases current and may damage the LED.

How do I read resistor color codes?

The first two bands represent digits, the third is a multiplier, and the fourth is tolerance (gold = 5%, silver = 10%). Our tool displays the correct colors for your resistor value.