Everyday · 4 min read

How to Estimate Your Electricity Bill

Written by Muhammad Ajmal · Last reviewed 2026-08-06

Most electricity bills are the sum of many individual appliances running for different amounts of time each day. You can estimate the cost of any single appliance, or your whole bill, with our electricity calculator, and the underlying math is straightforward once you know the formula.

The formula: watts to kilowatt-hours

Electricity is billed in kilowatt-hours, or kWh, which is a measure of energy used over time. To find kWh, multiply an appliance's wattage by the hours it runs, then divide by 1000, since a kilowatt is 1000 watts. A 1500 watt space heater running 4 hours a day uses 6 kWh that day. Multiply by your rate per kWh, commonly somewhere between $0.10 and $0.30 depending on where you live, to get the cost.

Worked example

Take that same 1500 watt heater at $0.16 per kWh. Daily cost is 6 kWh times $0.16, or $0.96. Over a 30 day month, that is $28.80. A small change in the rate makes a real difference at scale: the same heater at $0.30 per kWh would cost $54 a month instead.

Finding an appliance's wattage

Wattage is usually printed on a label on the appliance itself, on the underside or back, or in the manual. If only amps and volts are listed, multiply them together to get watts. A device pulling 5 amps at 120 volts uses 600 watts. Appliances with a motor or compressor, like refrigerators and air conditioners, do not run continuously even when powered on, so their real average wattage is lower than the rated maximum.

Appliances that use the most electricity

• Central air conditioning and electric heating, often 1500 to 3500 watts, running for hours at a time
• Water heaters, typically 3000 to 4500 watts, though usage is intermittent rather than continuous
• Clothes dryers, generally 2000 to 3000 watts per cycle
• Refrigerators, only 100 to 400 watts, but running nearly all day every day

A refrigerator's low wattage but constant runtime often adds up to a similar monthly cost as a dryer's high wattage but short runtime, which is why total hours of use matters as much as the wattage figure by itself.

Estimating your full monthly bill

To estimate a whole bill rather than one appliance, add up the daily kWh for everything you run regularly: lighting, HVAC, kitchen appliances, electronics, and anything else on a predictable schedule. Multiply the total by your rate and by the number of days in the billing period. This will not be exact, since usage varies day to day, but it gets you within a reasonable range and shows which appliances are driving the bulk of the cost.

Where estimates go wrong

The most common mistake is using an appliance's peak or startup wattage as if it ran at that level the whole time, when many devices cycle on and off or draw less power once they reach a set temperature. Standby power, the small amount devices draw even when off but still plugged in, is also easy to overlook, though it is usually a minor contributor compared to actively running appliances.

Lowering your estimated cost

Since cost scales directly with hours of use, reducing runtime has an immediate and predictable effect: cutting a heater's daily use from 4 hours to 2 hours cuts its cost in half. Lower wattage equipment, better insulation to reduce heating and cooling load, and running high draw appliances during off peak rate periods, where utilities offer them, are the other main levers.

Frequently asked questions