How Much Does Electricity Cost? Reading Your Bill in kWh

Electricity is billed in a unit most people never buy on purpose: the kilowatt-hour. One kWh is 1,000 watts running for one hour — a 1,500 W space heater burns through one every 40 minutes, while a 50 W device takes 20 hours to use the same amount. Your utility meters those kilowatt-hours and charges a rate for each one: about 17.5¢/kWh on average for US homes as of 2026, but anywhere from roughly 10¢ to over 40¢ depending on your state and plan.

That range is why "how much does electricity cost" has no single answer — but the cost of running any specific device does, and it comes down to three numbers you can actually find: the device's watts, the hours it really runs, and the rate on your bill. Multiply them correctly and you can put a dollar figure on anything with a plug.

The formula

Cost is energy times your rate, and energy is power times time. Watts get divided by 1,000 to become kilowatts, so the units line up with the kilowatt-hours your utility bills:

• kWh = (watts ÷ 1000) × hours per day × days
• cost = kWh × rate

Run the defaults through it — a 1,500 W device, 4 hours a day for 30 days, at $0.175/kWh:

• Energy: (1500 ÷ 1000) × 4 × 30 = 180 kWh
• Cost: 180 × $0.175 = $31.50 for the month — $1.05 a day

That is the entire calculation. Everything else in this guide is about feeding it honest inputs.

Step by step

1. Find the watts — the nameplate figure for a quick answer, the measured draw for an accurate one.
2. Count real runtime, not how long the device is plugged in.
3. Set the days to match the question: 30 for a month, 365 for a year.
4. Pull the rate from your bill, not from a national average.
5. Multiply — or let the calculator return the total, per-day, and per-month figures at once.

Your rate: read the bill, not the average

The rate is the input that varies most, and the bill does not hand it to you as one tidy number. There is usually a supply (energy) charge and separate delivery charges, often billed as several cents-per-kWh line items. Two ways to get your true rate:

• Add the line items. Every charge billed per kWh — supply plus each delivery component — sums to your all-in rate.
• Divide the bill. Take a full month's total and divide by the kWh used. If a month came to $31.50 across 180 kWh, your real rate is $31.50 ÷ 180 = $0.175/kWh. The Energy Bill Estimator works this way for exactly that reason.

The US average of 17.5¢/kWh is a fine placeholder, but with real rates spanning 10¢ to over 40¢, the average can be off by a factor of two in either direction for your house. Enter your own figure and the cost is honest rather than optimistic.

Watts × hours is the lever

The product of watts and hours is the whole game — halve either one and you halve the cost. Three devices at the same $0.175 rate make the point:

• The 1,500 W heater at 4 h/day costs $31.50 a month.
• The same heater at 8 h/day uses 360 kWh and costs $63.
• A 50 W device running 24/7 uses 1.2 kWh a day — $6.30 a month.

The last bar is the catch: a high-wattage device used briefly can cost less than a low-wattage one left on forever. A 1,000 W microwave running a few minutes a day barely registers, while the modest always-on box quietly outspends it. When you hunt for savings, look for the big watts × hours products, not just the big watts.

Nameplate watts vs the real draw

The wattage on the label or sticker is the maximum, and many devices use less in normal operation. If the label only lists amps, convert it: watts = volts × amps, so a 12 A device on a 120 V circuit draws about 1,440 W.

The bigger gap is cycling. Motor-driven, thermostat-controlled appliances — refrigerators, air conditioners — switch on and off, so their average draw sits well below the nameplate. A fridge is plugged in around the clock, but its compressor only works about a third of the time. Air conditioners cycle the same way, which is one reason getting the AC size right matters for the bill and not just for comfort.

For a quick estimate, the nameplate is a safe overestimate. For accuracy, a $15 plug-in meter (a Kill A Watt and the like) reads the actual draw at the outlet — and if you want to line up several appliances side by side, the Appliance Energy Calculator runs the same math across your whole list.

Be honest about hours and days

Runtime is where estimates quietly inflate or deflate. A space heater that is "on all evening" runs five or six hours, not twenty-four. A device being plugged in is not the same as it running. And the days input should match the question you are asking: 30 for a monthly cost, 365 for a yearly one.

Phantom load: the always-on tax

Plenty of devices draw power while switched "off" — TVs, chargers, game consoles, anything with a clock or a standby light. The draw is small, one to five watts, but it runs 24 hours a day, every day.

Put the formula on a 5 W standby draw: (5 ÷ 1000) × 24 × 365 = 43.8 kWh a year, which at $0.175/kWh is about $7.67 a year — for one device doing nothing. Across a house full of them, phantom load adds up to tens of dollars a year.

The calculator captures it directly: enter the standby watts and 24 hours a day, and the always-on draw gets a dollar figure like everything else.

Common mistakes to avoid

• Using the national average rate — real rates span 10¢ to 40¢+, so the average can be wildly wrong for your house.
• Forgetting the delivery charges — the supply rate alone makes every estimate optimistic.
• Taking nameplate watts for cycling appliances — fridges and ACs average far below the label.
• Counting plugged-in time as runtime — the "all evening" heater ran five hours.
• Ignoring standby draw — one to five watts, but it never stops.

Divide the watts by 1,000, multiply by real hours and the right number of days, then multiply by the rate your bill actually charges. That one line prices a heater, a fridge, a console on standby, or anything else with a plug — and with your true rate in it, the estimates match the bill.