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Work out watts, amps and Ohm’s Law calculations in one place

Knowing how to convert watts to amps is essential to prevent electrical fires, avoid tripping circuit breakers, and choosing the right cables.

Our tool brings together three common electrical calculations so you can check power, current, voltage and resistance without switching between separate tools.

Simply enter the figures you do know and get the answer you need in moments.

Why it matters

  • Every circuit in your home has a maximum current (amps) that it can handle safely.
  • Plugging high-wattage items into low-amp extension leads generates dangerous heat.

If you know the watts and amps involved, you can work out if you can use multiple appliances simultaneously.

The Formula Amps x Volts = Watts
Result:
The Formula Watts / Volts = Amps
Result:
The Formula Current x Resistance = Voltage
Result:
The Formula Voltage / Resistance = Current
Result:
The Formula Voltage / Current = Resistance
Result:

What are Amps, Volts and Watts?

Amps

Amps measure the flow of electricity as an electric current.

You can think of electric current as like the flow of water through a hosepipe.

The more water flowing through the hosepipe, the stronger the current is.

Volts

Volts are the measurement used to determine how much force is needed to cause the electric current to flow.

You can think of volts as like water pressure in a hosepipe, it makes the water flow.

Watts

Amps multiplied by Volts equals Watts, the measurement to determine the amount of energy.

The higher the wattage is, the more power and output from the appliance.

This is like the amount of water being released by a hosepipe.

AC and DC power systems

‘AC’ and ‘DC’ labels describe the types of current flow in a circuit. For direct current (DC) the electric current flows only in one direction.

But in alternating current (AC) the electric current changes direction at 50 times per second (50 Hz or hertz) in the UK supply.

An example of direct current is a battery-powered torch. Alternating current (AC) is used for mains-connected appliances as well as a house's overall electrical supply.

Read our guide to the current ratings of commonly-used domestic appliances

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Please note!

If you have an electrical project in the home, seek out professional advice first.

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What is Ohm's Law?

Ohm’s Law consists of three mathematical equations that explain the relationship between voltage, current and resistance.

If you know two of these values, you can calculate the third using Ohm’s Law.

The law is usually applied to DC (direct current) circuits but can also be applied to many AC (alternating current) circuits if they are mainly resistive.

It's named after Bavarian mathematician and physicist Georg Ohm, who first came up with it in 1827.

Voltage, current, and resistance explained

  • Voltage is the pressure from a power source (for example, a battery) that pushes current through a circuit.
  • Current is the flow of electrons through a conductor.
  • Resistance is the opposition that a conductor (wire) offers to the current flow.

As a general rule, resistance increases the longer the wire is, and decreases the thicker it is.

Each of these values can affect the others. For example, if there is too much resistance in a circuit, the voltage will drop or the current won’t flow as well.

Powering Change

Each year, we run consumer campaigns to increase awareness of the dangers of electricity. We want to help you make simple changes so you can stay safe in your home. Our campaigns are always informed by the latest consumer research and analysis of Government data.

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