Resistors & LEDs
Everything for the most common beginner topic in electronics, organized by what you're trying to do — run the numbers, decode a part, or understand why the maths works. Every tool is fully client-side; every figure is sourced.
Calculate
TransactionalPlug in numbers, get the answer — the everyday resistor maths.
LED Resistor Calculator Size the series resistor that keeps an LED from burning out (with the E24 standard value and power rating). Open tool → Ohm's Law Calculator Know any two of V / I / R / P and get the other two instantly. Open tool → Voltage Divider Calculator Two resistors split a voltage in proportion — solve Vout, current and power. Open tool → Series / Parallel Resistor Calculator Equivalent resistance of resistors in series or parallel. Open tool →
Decode & look up
ReferenceRead a part, or snap a value to something you can actually buy.
Resistor Color Code Decoder Pick the bands and read off resistance and tolerance (4 / 5 / 6 band). Open tool → Nearest E-Series Value Snap a computed value to the closest off-the-shelf standard (E6–E96). Open tool → E-Series Standard Values Browse every preferred value per series, plus a standard-value checker. Open tool →
Understand the why
LearnThe concepts behind the numbers — fact-dense guides, not fluff.
LED current-limiting resistor: theory & sizing Why an LED needs a resistor, why to round the standard value up, and how to pick the power rating. Read the guide → LED forward voltage chart by color Typical Vf for red through UV, and how it drifts with current and temperature. Read the guide → How to read resistor color codes The digit / multiplier / tolerance / temp-coefficient tables, and how to find band 1. Read the guide →
Prefer a step-by-step chain? See the digital-logic tracks →
Combinational logic series