kWh Bill Estimator

A single device's running cost only tells part of the story, a real electric bill is the sum of everything running in a home. This calculator lets you list out multiple devices, each with its own wattage, daily runtime, and quantity, then adds them all up into one estimated monthly and yearly bill.

It also breaks the total down by device, so it's easy to see which ones are actually driving the number up. If you only want the running cost of a single device, this site's Electricity Cost Calculator is a quicker, simpler version of the same math.

How does this calculator work?

Enter your electricity rate per kilowatt-hour and any fixed monthly base fee your utility charges regardless of usage.

Add a row for each device or appliance: a name, its wattage, how many hours a day it runs, and how many you have (four lamps at once, for example, rather than adding four separate rows).

For each device, the calculator computes daily energy the same way the single-device calculator does: kWh per day = (watts × hours × quantity) ÷ 1,000, folding quantity in as a multiplier since four identical lamps use four times the energy of one.

Each device's daily figure is scaled to a month (× 30) and multiplied by your rate to get that device's monthly cost, which is what populates the per-device chart and table.

All devices' monthly costs are added together, then the flat base fee is added once at the end (not per device, since it doesn't depend on usage) to produce the total estimated monthly bill, and that figure is multiplied by 12 for the yearly estimate.

For more on how base fees and tiered pricing show up on a real bill, see PG&E's tiered rate plan explainer, and for efficiency comparisons when swapping out devices, ENERGY STAR's lighting and appliance guide.

Worked example

A central AC unit (3,500W, 8 hrs/day), a refrigerator (150W, running effectively 24 hrs/day), and four lamps (100W each, 6 hrs/day), on a $0.15 per kWh rate with a $10 base fee.

Total energy used

≈957 kWh/month

Estimated monthly cost

≈$153.55

Estimated yearly cost

≈$1,842.60

How the numbers work

Each device's monthly kilowatt-hours come from watts times hours times quantity times 30 days, divided by 1,000.

The AC alone accounts for the largest share of the bill here (840 kWh, about $126 a month) since it combines high wattage with long daily runtime, while the lamps and refrigerator contribute smaller amounts individually.

Adding up individual devices this way usually reveals that a small number of high-wattage, long-running appliances (AC, heating, water heaters, electric dryers) account for most of a bill, while numerous small electronics add up to relatively little.