Calculate electrical resistance from voltage and current, voltage and power, or power and current. This resistance calculator estimates ohms, kilohms, megohms, current, voltage, and power using Ohm's Law and electrical power formulas.
Voltage and current:
Enter volts and amps. The calculator uses R = V ÷ I.
Voltage and power:
Enter volts and watts. The calculator uses R = V² ÷ P.
Power and current:
Enter watts and amps. The calculator uses R = P ÷ I².
A resistance calculator helps estimate ohms when you know voltage, current, or power.
It can help with resistor sizing, LED circuits, electronics projects, DC circuits, load estimates, component checks, power calculations, and basic electrical troubleshooting.
Your result shows estimated resistance, ohms, kilohms, megohms, voltage, current, power, the formula used, resistance category, scenario comparisons, and a calculation summary based on the values entered.
Use R = V ÷ I when you know voltage and current. Divide volts by amps to get ohms.
Use R = V² ÷ P. Square the voltage, then divide by power.
Use R = P ÷ I². Square the current, then divide power by that value.
No. Resistance applies directly to DC circuits and simple resistive loads. Impedance is used in AC circuits and can include resistance, capacitance, inductance, and frequency effects.