What formula is used?

R = V / I (Ohm's Law) when voltage is provided. R = P / I² when power is provided instead of voltage.

What units does this calculator use?

Current in amperes (A), voltage in volts (V), power in watts (W), and resistance in ohms (Ω).

Can I enter milliamps?

Yes. Convert milliamps to amps first by dividing by 1000 (e.g., 500 mA = 0.5 A).

What if I enter zero for current?

Division by zero is undefined. The calculator will display an error if current is zero.

Does this work for AC circuits?

For AC circuits this gives impedance magnitude, not pure resistance. Use it as an approximation for resistive loads only.

Is 1 ohm the same as 1 amp?

No. An ohm (Ω) measures resistance and an amp (A) measures current — different quantities. They are linked by Ohm's Law: at 1 volt, 1 ohm of resistance allows exactly 1 amp of current (I = V / R).

Amps to Ohms Calculator

Calculate resistance in ohms from current and voltage (R = V / I) or current and power (R = P / I²).

Enter Values

Current (A) *

Calculate using

Voltage (V)

Enter current and voltage or power, then click Calculate.

Resistance

0 Ω

Formula Applied

Parameter	Value

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Summary

This calculator converts amperes to ohms using Ohm's Law (R = V / I) or the power formula (R = P / I²). Enter current along with voltage or power to instantly find resistance in ohms.

How it works

Enter the current in amperes (A).
Enter either the voltage in volts (V) or the power in watts (W).
Read the resistance in ohms — the tool uses R = V / I, or R = P / I² when you supply power.

Use cases

Determine the resistance of a circuit element given its supply voltage and operating current.
Size a resistor to limit current in an LED or other low-power component.
Verify that a heating element's resistance matches its rated wattage and current draw.
Troubleshoot electrical faults by comparing calculated resistance to measured values.

Frequently Asked Questions

Last updated: 2026-05-23 · Reviewed by Nham Vu