Why do LEDs need a current-limiting resistor?

LEDs are current-driven devices with very low internal resistance. Without a resistor, current would spike far above the rated maximum, destroying the LED almost instantly.

How do I find the forward voltage of my LED?

Check the LED datasheet. Typical forward voltages are: red ~2.0 V, green ~2.2 V, blue/white ~3.0-3.4 V. If unknown, 2.0 V for red/yellow and 3.3 V for blue/white are safe estimates.

What wattage resistor should I use?

Calculate power as P = I squared times R. Then choose a resistor rated at least double the calculated power for safety. Most LED circuits use 1/4 W resistors.

LED Resistor Calculator

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About LED Resistor Calculator

Every LED needs a current-limiting resistor to prevent burnout. This calculator uses R = (Vs - Vf) / I, where Vs is the supply voltage, Vf is the LED forward voltage, and I is the desired forward current. It selects the nearest standard resistor value, computes actual current and power dissipation, and recommends a resistor wattage rating.

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FAQ

What electrical engineering calculations can this tool perform?

This tool handles LED resistor sizing (R = (Vs - Vf) / I), wire voltage drop (NEC Chapter 9 tables), conduit fill analysis (NEC fill limits), and power factor correction (power triangle with capacitor sizing).

Are the results accurate?

Yes. All calculations use deterministic algorithms and NEC/IEEE reference data. Every result is mathematically guaranteed to be correct.

Is this electrical engineering calculator free?

Yes! All electrical engineering calculations are completely free with detailed step-by-step explanations. No account required.

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