Ohm's Law Current Calculator

Created by Arturo Barrantes
Reviewed by Luis Hoyos
Last updated: Jun 05, 2023

The Ohm's Law Current Calculator will help determine the electrical current flowing through an energized system. It can also help you design your electrical home installations. Do you want to install a new bell, maybe a new water pump? Keep reading to find out how to calculate current using Ohm's law.

What is electrical current?

We will start exploring the electric current definition. Electric current represents the flow of electrons through a conductor. If more electrons are flowing, we will have a higher current value. The International System of Units (SI) defines the ampere (A\text{A}) as the unit to measure electrical current.

But why do electrons move? That is because of voltage. The voltage unit is the volt (V\text{V}), and its work consists of pushing electrons through the conductor. Conversely, conductors, like copper cables, provide friction to the electron's flow. That is called resistance, and the SI measures it in ohms (Ω\text{Ω}).

The scientific world has defined Ohm's law as the relationship between current, voltage, and resistance.

Ohm's law for current

The Ohm's law arranged for getting the current is:

I=VR,I = \frac{V}{R},


  • II — Current, in amperes (A\mathrm{A});
  • VV — Voltage, in volts (V\mathrm{V}); and
  • RR — Resistance, in ohms (Ω\mathrm{Ω});

You can also express II in terms of the electrical power (PP):

I=PV,I = \frac{P}{V},

where PP is the power in watts (W\mathrm{W});

How to calculate current using Ohm's law?

Whenever you buy equipment, you usually will see the voltage at which it has to be connected and the power it consumes. Hence, we will use Ohm's law for current to determine how much amperage it needs. You can also try our Ohm's law current calculator.

  1. Find out the power consumption of the equipment. Assume we have a hair dryer of 2000 W and a 220 volts house grid.

  2. Divide power by voltage as per current Ohm's law

  3. The result is 9.09 amperes of current.

In case you want to build a cable extension, you can use our wire size calculator to determine the cable diameter you need.

Other tools like this Ohm's law current calculator

If you are interested to learn more about the science and math of Ohm's law, you may want to visit our other tools related to this fundament of electromagnetism:


How much current do we have in 220 volts?

It depends on the resistance of the wire that we use to transport the current. As per Ohm's law current, if resistance is zero, you could get infinite current from a 220 volts plug. Besides, a cable's resistance is affected by its diameter and material. A 6 AWG wire (approximately 0.25 inch) can safely transfer up to 52 amperes.

How many amps do I need for my house?

It depends on how much equipment you plan to plug. You can try Omnicalculator's Ohm's Law Current tool or do as follows:

  1. Determine all the power you require. Let's say 10,000 watts (refrigerators, microwave, hair dryer, among others).
  2. Assuming your house provides 220 volts, divide the total power by the voltage as per current Ohm's law.
  3. The result is 45.45 amperes.
Arturo Barrantes
Electric circuit model with a resistor
Voltage (V)
Resistance (R)
Power (P)
The result
Current (I)

You do know how to find resistance? If not, here are some calculators that you might find helpful:

Series resistor calculator;

Parallel resistor calculator; and

Wire resistance calculator.
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