9V Battery Powering a Red LED — What Resistor?
To power a red LED (2.0V forward voltage) from a 9V battery at 20mA, you need a 350-ohm resistor.
How to use this tool
- Enter supply voltage (vs), led forward voltage (vf) and led current in the fields above.
- Results update instantly as you type — or click Calculate.
- Read your series resistance and the full breakdown beneath it.
Find the right resistor to protect a red LED powered from a standard 9-volt battery.
Frequently asked questions
- What forward voltage should I use?
- Red and yellow LEDs are typically 1.8–2.2 V. Green, blue, and white LEDs are usually 3.0–3.5 V. Check your LED's datasheet for the exact value.
- What current should I use?
- Standard 5 mm through-hole LEDs are rated for 20 mA maximum. A common value for a bright but conservative drive is 10–15 mA.
- Should I round up or down to the nearest standard resistor value?
- Round up to the next E12/E24 standard value to keep current at or below the rated maximum. Rounding down would exceed the LED's current rating.