How Much Does It Cost to Run an Appliance? The Simple Formula

A space heater, a dehumidifier, a gaming console left on all day: which ones actually move your electric bill? You do not need to guess. Three numbers, the device's wattage, how many hours you use it, and your price per kilowatt-hour, give you a monthly cost in about a minute.

1. The formula

1. Find the wattage. It is usually on a label on the back or bottom of the device, or in the manual.
2. Convert to kilowatt-hours. Watts x hours used per day / 1,000 = kilowatt-hours (kWh) per day.
3. Multiply by your rate. kWh per day x days x price per kWh = cost.

Your price per kWh is on your utility bill. If you want a national benchmark, the U.S. Energy Information Administration reports that the average residential electricity price was 18.31 cents per kWh in July 2026. State averages range widely around that, so your own rate is always the better number.

2. Worked examples at 18.31 cents per kWh

Two very different devices land on the same cost because the math only cares about watts times hours. A 1,500-watt heater used 4 hours and a 500-watt dehumidifier used 12 hours both use 180 kWh a month. Run that space heater 8 hours a day instead and the cost doubles to about $66 a month.

The label wattage is often the maximum. Devices with thermostats or cycling compressors, like heaters, refrigerators, and dehumidifiers, do not draw full power every minute, so treat the result as an upper estimate. A plug-in electricity usage meter gives a measured number if you want precision.

3. The always-on load

Some costs come from devices you are not using at all. The Department of Energy's Energy Saver guide says many consumer electronics continue to draw power even when switched off, which could add an extra 5% to 10% to your monthly utility bill.

On a $150 monthly electric bill, that is $7.50 to $15 a month, or $90 to $180 a year. Plugging a TV, console, and sound system into a power strip you switch off at night is a low-cost way to recover part of it. The guide also suggests asking your cable or satellite provider for an ENERGY STAR certified set-top box, which it says is 25% more efficient than conventional models.

4. Lighting, briefly

Lighting is spread across many small loads. The Department of Energy says the average U.S. household has about 70 light bulbs, and that one ENERGY STAR certified LED bulb uses up to 90% less energy than old incandescent bulbs and can save about $55 in electricity costs over its lifetime. If you still have incandescent bulbs in the fixtures you use most, those are the ones to replace first.

5. Using the formula to make decisions

• Before buying a space heater, price the hours you would actually run it. A whole season of heavy use can rival the cost of fixing the draft that made the room cold.
• When an old appliance runs constantly, like a second refrigerator in the garage, estimate its cost per year and compare it with what you get from it.
• When comparing new models, the Department of Energy suggests using the EnergyGuide label or energystar.gov to compare models before you buy.
• When your bill jumps, list devices that are new or used more this month and run the formula on each.

6. Watch for rate tiers and time-of-use pricing

Some utilities charge more per kWh above a usage threshold, or at certain hours of the day. If your bill shows tiered or time-of-use rates, use the rate that applies when the device actually runs. Shifting a flexible load like a dehumidifier or a dishwasher to off-peak hours can lower the cost without using any less electricity.

7. Key takeaways

• Cost = watts x hours / 1,000 x days x price per kWh.
• The U.S. average residential electricity price was 18.31 cents per kWh in July 2026; your bill has your exact rate.
• A 1,500-watt space heater run 4 hours a day for 30 days uses 180 kWh, about $33 at the average rate.
• Electronics drawing power while off can add 5% to 10% to a monthly bill.
• An LED bulb uses up to 90% less energy than an incandescent and can save about $55 over its life.