What is a volts to amps calculator?
A volts to amps calculator converts an electrical voltage, measured in volts (V), into the current that flows through a circuit, measured in amps (A), once you know the resistance of that circuit in ohms (Ω). Voltage is the electrical “pressure” that pushes charge through a conductor, resistance is how much the conductor opposes that flow, and current is the resulting rate at which charge moves. Working out the current is useful for sizing wires, choosing fuses and breakers, and checking that a component will not be overloaded.
Unlike a watts-to-amps conversion, which starts from power, this calculator starts from resistance. That makes it a direct application of Ohm’s law rather than the power equation.
How does it work?
The relationship between voltage, current, and resistance is described by Ohm’s law. For a simple resistive circuit, the current equals the voltage divided by the resistance:
where is the current in amps (A), is the voltage in volts (V), and is the resistance in ohms (Ω). The resistance must be greater than zero, because dividing by zero resistance has no meaningful answer.
To use the calculator:
- Enter the voltage across the circuit in volts.
- Enter the resistance of the circuit in ohms.
- The calculator instantly shows the current in amps. The result appears only when both values are present and the resistance is not zero.
Worked examples
Consider a 12-volt supply driving a 4-ohm load. The current is:
A 120-volt supply across a 60-ohm resistor gives:
And a 9-volt battery connected to a 3-ohm resistor produces:
Practical notes
Ohm’s law applies cleanly to resistive (ohmic) components such as resistors and heating elements, where resistance stays roughly constant. For components whose resistance changes with temperature, frequency, or applied voltage, the calculated current is an approximation at the operating point you choose.
If you know power instead of resistance, use the watts-to-amps conversion at https://www.mega-calculator.com/physics/watts-to-amps/ , or work in the other direction with amps-to-watts at https://www.mega-calculator.com/physics/amps-to-watts/ . To find power directly from voltage and current, see volts-to-watts at https://www.mega-calculator.com/physics/volts-to-watts/ .
FAQ
Why does the result disappear when I enter 0 ohms?
A resistance of zero would mean dividing the voltage by zero, which is undefined and physically represents a short circuit, so the calculator hides the result until you enter a resistance greater than zero.
Does this work for AC circuits?
It works directly for DC circuits and for purely resistive AC loads. For reactive AC loads that include inductance or capacitance, you would replace resistance with impedance and account for the phase relationship between voltage and current.