Electronics calculators
7 free tools
Bench-side math for anyone building circuits. Decode a resistor's color bands, pick the right series resistor for an LED, design a voltage divider, or figure out how long a battery will last — no datasheet hunting required.
Estimate a battery's runtime from its capacity, the load current, and a real-world efficiency factor.
Calculate the energy stored in a capacitor and its charge from capacitance and voltage.
Size the series resistor an LED needs from your supply voltage, its forward voltage, and current.
Find the RC time constant, the 63% charge time, and the full-charge time from resistance and capacitance.
Pick the color of each band and read off a resistor's resistance and tolerance.
Combine any number of resistors in series or parallel to find their total resistance.
Find the output voltage and current of a two-resistor voltage divider from Vin, R1, and R2.
Frequently asked questions
Who are these electronics calculators for?
Hobbyists, students, and makers wiring up breadboards or Arduino projects. They handle the everyday arithmetic — Ohm's law, resistor codes, RC timing — so you can spend your time building instead of shuffling formulas.
Do I need to convert units first?
Not usually. Each tool tells you the unit it wants, like milliamps for LED current or microfarads for capacitance, and it handles the conversion to base units internally before doing the math.
Are the standard resistor values realistic?
Yes. The LED tool snaps its result to the nearest E12 value, which is the series most cheap through-hole resistors actually come in, so the number it suggests is one you can really buy.