What makes this different
This calculator solves voltage, current, resistance, and power in one place, then adds a resistor heat check so the answer is usable on a breadboard or PCB.
Ohm's Law Calculator
Ohm's law calculator for real circuit checks
Core formulas
Use V = I x R for voltage, I = V / R for current, R = V / I for resistance, and P = V x I for power dissipation.
Design tip
When the power result approaches a resistor's rated wattage, choose a higher wattage part. A 2x margin is a practical starting point for hobby electronics.