Electrical calculator
LED Resistor Calculator
Calculate the current-limiting resistor needed for an LED.
About the led resistor calculator
The LED resistor calculator finds the current-limiting resistor needed to safely power an LED from a given supply voltage.
How to use this calculator
- 1
Enter supply voltage
Enter your power supply voltage.
- 2
Enter LED specs
Enter the LED forward voltage and desired current.
- 3
View results
See the exact resistor value, nearest E12 standard value, and power rating.
How the calculation works
R = (Vsupply − Vled) ÷ Iled. Power rating = (Vsupply − Vled) × Iled.
Example: 5V supply, 2V LED, 20mA: 150Ω resistor, 0.06W.
Safety first
These calculators provide estimates based on standard formulas and NEC guidelines. Always verify results with a licensed electrician before making installations. Electrical work can be dangerous — never work on live circuits, and always follow local building codes and regulations.
Understanding electrical units
Voltage (V) is electrical pressure, current (A) is flow rate, resistance (Ω) opposes flow, and power (W) is the rate of energy use. Ohm's law (V = I × R) relates the first three, while power formulas (P = VI, P = I²R) connect all four. Understanding these relationships is key to safe electrical design.
Important limitations
This tool provides a mathematical estimate based only on the values entered. It does not account for regulations, taxes, lender fees, market conditions, or individual circumstances. Results are for planning purposes only — consult a qualified professional for regulated, medical, financial, or construction decisions.
Frequently asked questions about led resistor calculator
How accurate is the LED resistor calculator?+
The calculation follows the displayed formula and retains full numeric precision before formatting the result.
Can I use the result professionally?+
Use it as a planning estimate. Confirm regulated, medical, financial, or construction decisions with a qualified professional.