Electricity Bill Calculator

Electricity bills charge for energy, not power — kilowatt-hours, not watts. This converts an appliance's wattage and hours of use into a running cost per day, month and year, so you can see what's actually driving the bill rather than guessing from the wattage label alone.

The formula, and why watts alone don't tell you the cost

cost = (watts ÷ 1000) × hours × rate. A 1500W heater running 5 hours a day uses 7.5 kWh a day, and at $0.15/kWh that's $1.13/day, or roughly $33.75/month if it runs every day. A 100W lamp left on 24 hours a day uses the same 2.4 kWh as that heater running for under 2 hours — appliance wattage on its own says nothing about the bill until it's multiplied by how long it actually runs.

Where the wattage number comes from

It's usually printed on the appliance's rating label, its power supply, or the plug — look for a number in watts (W) or, if only volts and amps are shown, multiply them together (V × A = W). Continuous loads like heaters, kettles, and older incandescent lighting draw close to their rated wattage the whole time they're on; cycling appliances like fridges and air conditioners only draw their rated wattage in bursts, so treat their nameplate figure as a rough upper bound rather than a constant draw.

Comparing several appliances

Adding more than one appliance builds a combined monthly total, which is the more useful question in practice — not 'what does the fridge cost' in isolation, but which of several running appliances is actually worth unplugging. A phone charger left plugged in typically draws under 1W idle; a space heater can be 1,000–1,500W running — the two are not remotely comparable contributors to a bill, even though both are 'always plugged in'.