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Electronics

Circuit calculators — Ohm’s law, voltage dividers, LED resistors, capacitors, and more.

10 tools

Ohm’s Law

Voltage, current, resistance, power.

Resistors (Series & Parallel)

Total resistance of resistors in series or parallel.

Resistor Color Code

Resistance and tolerance from the color bands.

Voltage Divider Calculator

Output voltage from two resistors in a divider.

LED Resistor Calculator

Series resistor value for an LED from supply and forward voltage.

Capacitor Energy Calculator

Energy and charge stored in a capacitor from capacitance and voltage.

RC Time Constant Calculator

Time constant τ = RC and the charge/discharge curve.

Capacitors in Series & Parallel

Total capacitance of capacitors wired in series or parallel.

Reactance Calculator

Capacitive and inductive reactance at a given frequency.

Battery Life Calculator

Estimate runtime from battery capacity and load current.

About electronics tools

The everyday calculations behind circuits — Ohm’s law, voltage dividers, LED series resistors, capacitor energy and RC time constants, series/parallel networks, and reactance. Each tool shows the formula and the working, for electronics coursework and hobby builds alike.

When to use these tools

Common electronics tasks and the tool that handles each one.

Frequently asked questions

Common questions about electronics — the concepts behind the tools above.

What is Ohm’s law?
Ohm’s law states that the voltage across a resistor equals the current through it multiplied by its resistance, written V = I × R. Rearranging it lets you find any one quantity from the other two, for example I = V ÷ R.
How do resistors combine in series versus parallel?
In series the resistances simply add, so the total is R1 + R2 + …, giving a larger value. In parallel the reciprocals add (1/R_total = 1/R1 + 1/R2 + …), so the combined resistance is always smaller than the smallest individual resistor.
What does a capacitor do in a circuit?
A capacitor stores energy in an electric field between two plates and opposes sudden changes in voltage. It blocks steady DC once charged but passes changing (AC) signals, which makes it useful for filtering, smoothing power supplies and coupling signals. Capacitance is measured in farads (F).
How do you read a resistor’s color code?
On a common 4-band resistor the first two bands are significant digits, the third is a multiplier (a power of ten), and the fourth is the tolerance. For example brown-black-red-gold means 1, 0, ×100 = 1000 Ω (1 kΩ) at ±5% tolerance.

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