Electricity Calculators & Tools
Free, practical tools for hands-on electricity — solve Ohm’s law, decode a resistor’s color bands, combine resistances, estimate battery life, size an LED resistor, and estimate a static charge.
Ohm's Law Calculator
Solve for voltage, current, resistance, or power from any two known values — the core relationship behind every DC circuit
Resistor Color Code Calculator
Decode a 4-band or 5-band resistor's color stripes into its resistance and tolerance using the standard EIA color code
Series/Parallel Resistance Calculator
Combine two or more resistors wired in series or parallel into a single total resistance
Battery Life Calculator
Estimate how many hours a battery will power a given current draw from its rated mAh capacity, with a real-world derating factor
LED Series-Resistor Calculator
Work out the resistor value and power rating needed to drive an LED safely from a supply voltage, with the nearest standard part
Static Charge Demo Guide
Estimate the capacitance and charge of a charged sphere — the physics behind a Van de Graaff generator — plus classic static demonstrations
LED Resistor Reference
Every common LED color at every common battery voltage in one table — the calculated resistor, the nearest real part, and what it actually delivers