This electronics calculator bundles the everyday circuit calculations — Ohm's law, voltage dividers, LED series resistors, and power — into one tool. It is built for hobbyists and students who need a quick, reliable answer when designing or debugging a small circuit.
Ohm's law and power
Ohm's law, V = I × R, ties voltage, current, and resistance together: knowing any two gives the third. Power follows as P = V × I (and equivalently I²R or V²/R). These relationships underpin almost every basic circuit decision — sizing a resistor, checking a current draw, or confirming a component will not overheat. The calculator lets you enter what you know and returns the rest.
Voltage dividers use two resistors to produce a fraction of the input voltage, output = input × R2 ÷ (R1 + R2), handy for setting reference voltages and scaling signals. The calculator solves the divider for whichever quantity you need.
Driving an LED safely
An LED needs a series resistor to limit its current, or it will burn out. The resistor value is (supply voltage − LED forward voltage) ÷ desired current. Get this wrong and the LED runs too dim or dies; the calculator works it out from your supply, the LED's forward voltage, and the target current, and shows the power the resistor will dissipate so you can choose an adequate rating.
Driving a red LED (2 V forward, 20 mA) from a 5 V supply.
- Voltage across the resistor = 5 − 2 = 3 V.
- Resistor = 3 V ÷ 0.02 A = 150 Ω.
- Power in the resistor = 3 V × 0.02 A = 0.06 W (a ¼ W resistor is fine).
Use a 150 Ω resistor (¼ W is plenty) to run the LED at 20 mA from 5 V.
