Electricity Cost Calculator

How to use the electricity cost calculator

1. Fill in the fields — they start with a worked example.
2. Read the answer, and the arithmetic shown beneath it.
3. Copy the results, or adjust the inputs to compare scenarios.

About this tool

Energy is power multiplied by time. A 100 W device left on for ten hours uses one kilowatt-hour, and a kilowatt-hour is the unit your electricity bill charges for — so the whole calculation is watts × hours ÷ 1000 × price.

What surprises people is which appliances actually cost money. Anything that makes heat dominates: kettles, ovens, tumble dryers, electric heaters and immersion heaters run at 2,000 to 3,000 W. Electronics barely register by comparison — a laptop at 50 W run continuously for a month costs less than a few loads of tumble drying.

Standby power is the opposite case, and worth checking rather than assuming. A single device drawing 2 W does cost almost nothing, but it draws it every hour of every day, and a household with twenty such devices is running a permanent 40 W load.

The wattage on an appliance's label is usually its maximum rather than its typical draw. A fridge rated at 150 W does not consume 150 W continuously — its compressor cycles, so actual consumption may be a third of that.

Common uses

• Working out what a heater or tumble dryer costs to run.
• Deciding whether an old appliance is worth replacing.
• Checking the real cost of leaving devices on standby.

Frequently asked questions

Which appliances cost the most to run?

Anything that produces heat — kettles, ovens, dryers, electric heaters. They draw 2,000 to 3,000 W, where electronics draw tens of watts.

Does standby power really matter?

Per device, barely. Across a household of twenty devices at 2 W each it is a permanent 40 W load, which is worth knowing but is not where the big savings are.

Why is my bill higher than this suggests?

The label wattage is usually a maximum, not a typical draw, and appliances like fridges cycle. Standing charges and tiered rates also sit outside this calculation.