Electricity Cost Calculator

How to use the electricity cost calculator

Enter the device’s power in watts, how many hours a day it runs, and over how many days, plus your electricity rate, and you get the cost to run it — over the whole period, per day, and per 30-day month. The rate is the input that varies most: the US residential average is about 17.5¢/kWh as of 2026, but it ranges from roughly 10¢ to over 40¢ depending on your state, so pull the rate from your own bill rather than trusting an average.

Watts can be the nameplate figure or the real draw. The number on the label or sticker is the maximum; many devices use less in normal operation, and motor-driven ones — refrigerators, air conditioners — cycle on and off, so their average draw sits well below the nameplate. For a quick estimate the nameplate is fine; for accuracy, a $15 plug-in meter (a Kill A Watt and the like) reads the actual draw at the outlet.

Be honest about hours and days. A space heater that’s “on all evening” runs five or six hours, not twenty-four; a fridge runs around the clock but its compressor only works about a third of the time. Set the days to match what you’re pricing — 30 for a month, 365 for a year — and the hours to real runtime, not how long the device is plugged in.

Phantom load is the quiet one. Plenty of devices draw power while switched “off” — TVs, chargers, game consoles, anything with a clock or a standby light. It’s small per device, one to five watts, but it runs 24 hours a day and adds up across a house. The calculator captures it if you enter the standby watts and 24 hours; that’s how you put a dollar figure on always-on draw.

The rate on your bill isn’t one tidy number. There’s usually a supply (energy) charge and separate delivery charges, often billed as several cents-per-kWh line items. Add the per-kWh components for a true rate, or divide a full month’s total by the kWh used for the real all-in figure — what the Energy Bill Estimator does. Enter that here and the cost is honest rather than optimistic.

The formula

Cost is energy times your rate, and energy is power times time. Watts are 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

Worked example with the defaults — a 1,500 W device, 4 hours a day for 30 days at $0.175/kWh: (1500 ÷ 1000) × 4 × 30 = 180 kWh, times $0.175 = $31.50. That’s $1.05 a day and, over a 30-day month, $31.50.

The lever that matters is watts × hours — halve either and you halve the cost. A high-wattage device used briefly (a 1,000 W microwave for a few minutes a day) can cost less than a low-wattage one left on forever (a 50 W device running 24/7 is 1.2 kWh a day, about $6.40 a month at the same rate).

Frequently asked questions

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