Electrical

kWh Calculator

Calculate how much energy (kWh) and money an appliance uses, daily, per billing period, and per year.

Formula Period Energy = Daily Energy × dReviewed Sep 8, 2026

How much does it actually cost to run something? This calculator converts an appliance's power draw and daily usage time into energy consumed in kilowatt-hours - the unit utilities actually bill - and, with your electricity rate, into a dollar cost per day, per billing period, and per year. Use it for appliances, lighting, tools, pumps, HVAC equipment, and standby loads. This is a genuinely different question from this site's Electrical Power Calculator, which computes power itself (watts) at a single instant, not energy consumed over time.

Calculation Bench

01Power

P · Appliance's power draw

02Hours per Day

h · Actual hours of power draw, not hours plugged in

03Days in Billing Period

d · Defaults to 30 (monthly estimate)

04Electricity Rate

$/kWh · Optional - leave blank to skip cost estimate

Solution

Enter power and hours of use to calculate energy and cost.

Period Energy = Daily Energy × d

Formula Sheet

E_{day} = \dfrac{P \times h}{1000}

E_{period} = E_{day} \times d

\$ = E_{period} \times \text{Rate}

$Cost per Period
PPower
hHours per Day
dDays in Billing Period
RateElectricity Rate

Variables & Units

Symbol	Variable	Description	Common Units
$	Cost per Period	Total electricity cost over the entered billing period.
P	Power	The appliance's power draw.	W, kW
h	Hours per Day	Actual hours of power draw per day.
d	Days in Billing Period	Number of days in the usage or billing period being estimated.
Rate	Electricity Rate	Your utility's price per kilowatt-hour, in dollars.

How to Use This Calculator

01Enter the appliance's power draw in watts - check the nameplate, or use the reference table below for a typical range.
02Enter how many hours per day it actually runs - not how many hours it's plugged in, but how many hours it's actually drawing power (a refrigerator cycles on and off, for instance).
03Enter the number of days in your billing period - 30 is the default for a monthly estimate.
04Enter your electricity rate in dollars per kWh, from a recent utility bill, to also get a cost estimate.
05Compare the result against your utility bill by adding major appliances one by one. If the total is much lower than the bill, look for HVAC runtime, water heating, standby loads, or tiered/time-of-use rates.

How the Formula Works

A kilowatt-hour is exactly what it sounds like: one kilowatt (1,000 watts) of power sustained for one hour. Energy in kWh is power in watts times hours of use, divided by 1,000 - a 1,000-watt appliance running for one hour uses exactly 1 kWh, the same as a 100-watt appliance running for ten hours.

Multiplying that daily energy figure by the number of days in your billing period gives total energy for the period, and multiplying by your rate (dollars per kWh) converts that into a dollar cost - the same arithmetic your utility uses to generate a bill.

The annual cost figure is always calculated from the daily energy value times 365 days, independent of whatever billing-period length you entered - so you get a genuine year-over-year cost comparison regardless of whether you entered a weekly, monthly, or any other period.

The biggest source of error in a real-world estimate isn't the arithmetic, it's the hours-per-day figure - a refrigerator's compressor might only run a third of the time even though it's plugged in 24 hours a day, so "hours of actual power draw" and "hours plugged in" are often very different numbers for cycling appliances.

For appliances with a known monthly energy label, reverse-check the runtime assumption: Daily hours = labeled monthly kWh × 1000 / (watts × billing days). That helps avoid overestimating cycling equipment by treating it as if it runs continuously.

Worked Example 01

60W incandescent bulb, 8 hours a day

Known

Power (P): 60 W
Hours per Day (h): 8
Days in Billing Period (d): 30
Electricity Rate: $0.16/kWh

Formula

Cost = Period Energy × Rate

Substitution

Daily = 60 × 8 / 1000 = 0.48 kWh, Period = 0.48 × 30 = 14.4 kWh, Cost = 14.4 × 0.16

Result

$2.30/month (≈$28.03/year)

A 60 W bulb run 8 hours a day uses 0.48 kWh daily, 14.4 kWh over a 30-day month, costing about $2.30 at 16 cents per kWh - roughly $28 a year if that usage pattern holds steady.

Worked Example 02

1,000W window AC unit, 6 hours a day

Known

Power (P): 1,000 W
Hours per Day (h): 6
Days in Billing Period (d): 30
Electricity Rate: $0.168/kWh

Formula

Cost = Period Energy × Rate

Substitution

Daily = 1000 × 6 / 1000 = 6 kWh, Period = 6 × 30 = 180 kWh, Cost = 180 × 0.168

Result

$30.24/month (≈$367.92/year)

A 1,000 W window air conditioner run 6 hours a day uses 6 kWh daily, 180 kWh over a month - a much larger cost than the light bulb example, illustrating how much power draw (not just hours of use) drives energy cost.

Applications

01Estimating the monthly or annual cost of running a specific appliance
02Comparing energy cost between two appliances or usage patterns (e.g. an older vs. a newer, more efficient model)
03Sanity-checking a utility bill against expected usage for known appliances
04Estimating standby energy use for devices that stay plugged in all day

Typical Appliance Wattage and Runtime Notes

Appliance	Typical Wattage	Runtime note
LED light bulb	8-12 W	Use actual hours the light is on.
Incandescent light bulb	40-100 W	Usually close to nameplate wattage.
Laptop computer	50-75 W	Charging and heavy CPU use can raise draw.
LED/LCD television	30-100 W	Use viewing hours, not plugged-in hours.
Refrigerator (running average)	150-250 W	Compressor cycles; do not enter 24 hours at peak watts.
Microwave oven	600-1,200 W	High wattage, but usually short runtime.
Window air conditioner	500-1,500 W	Actual cost depends heavily on duty cycle.
Space heater	1,000-1,500 W	Often near full draw while heating.
Hair dryer	800-1,800 W	Short runtime keeps kWh modest.

Assumptions

01Power draw is treated as constant across every hour of use - a real appliance's draw often varies (a refrigerator compressor cycling, a variable-speed motor ramping), so this is an average-use estimate, not a precise metered figure.
02The electricity rate entered is a flat per-kWh figure - it doesn't model tiered pricing, time-of-use rates, or demand charges some utilities apply.

Where This Model Stops

01Does not account for tiered or time-of-use electricity pricing, where the rate itself changes based on total usage or time of day.
02Does not include fixed utility charges (connection fees, taxes) that appear on a real bill alongside the per-kWh energy charge.
03Appliance wattage figures in the reference table are typical ranges, not a substitute for the specific nameplate rating on your actual appliance.
04Does not estimate demand charges or peak-kW charges used on some commercial utility bills.

References

[1]
What is a kilowatt-hour and what can it power?
U.S. Energy Information Administration
Reference for the kWh unit definition and the energy = power × time relationship used in this calculator.

Frequently Asked Questions

What's the difference between this and the Electrical Power Calculator?

Electrical Power Calculator computes power itself - watts, at a single instant, from voltage/current/resistance. This calculator takes that power figure and multiplies it by time and a utility rate to get energy consumed and cost, which power alone doesn't tell you - a 1,000 W device run for one second uses far less energy than a 100 W device run all day.

Should I use the appliance's nameplate wattage or its actual average draw?

Actual average draw gives a more accurate estimate when the two differ, which happens most for cycling appliances like refrigerators and thermostatically-controlled heaters/coolers - their nameplate rating is the peak draw, not what they average over time. For a constant-draw device like a light bulb or a space heater on a single setting, nameplate wattage is a good match for actual draw.

Why is my actual utility bill different from this calculator's estimate?

Utility bills often include tiered pricing (rate changes based on total monthly usage), time-of-use rates (different price by time of day), and fixed charges (connection fees, taxes) beyond the flat per-kWh energy charge this calculator uses - plus your actual hours-of-use figure may differ from what was entered.

How much does electricity cost per kWh in the US?

The US average is roughly $0.17/kWh, but actual rates vary widely by state and utility - from around $0.10/kWh in some states to over $0.40/kWh in others. Always use the rate from your actual utility bill for an accurate cost estimate rather than a national average.

Can I use this calculator for a whole-house electricity bill?

Yes, but only as a bottom-up estimate: calculate major loads one at a time, then add the period kWh values. It will not automatically capture hidden loads, HVAC cycling, water heating, standby power, tiered pricing, fixed fees, taxes, or solar/net-metering adjustments.

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