What formula converts watts to kilowatt-hours?

kWh = (W × h) / 1000. Multiply the power in watts by the time in hours to get watt-hours, then divide by 1,000 to convert to kilowatt-hours.

What is a kilowatt-hour?

A kilowatt-hour (kWh) is an energy unit equal to 1,000 watts used continuously for one hour. It is the standard unit utility companies use to measure and bill household and commercial electricity consumption.

How do I convert minutes or days to hours?

Divide minutes by 60 to get hours (e.g., 45 minutes = 0.75 h). Multiply days by 24 to get hours (e.g., 3 days = 72 h).

How many kWh does a 1,500-watt heater use in 8 hours?

kWh = (1500 × 8) / 1000 = 12,000 / 1000 = 12 kWh.

What is the difference between watts and kilowatt-hours?

Watts (W) measure power — the rate of energy use at any instant. Kilowatt-hours (kWh) measure energy — the total electricity consumed over time. A 100 W bulb burning for 10 hours uses 1 kWh.

How do I estimate monthly electricity cost from watts?

Calculate daily kWh = (W × daily hours) / 1000. Multiply by 30 for monthly kWh, then multiply by your electricity rate ($/kWh). This calculator does all that automatically when you enter your rate.

Watts to Kilowatt Hours Calculator

Name: Watts to Kilowatt Hours Calculator
Availability: InStock
Author: Nham Vu

Enter power in watts and duration in hours to instantly calculate energy consumption in kilowatt-hours (kWh).

Input Values

Power (W)

Time (hours) e.g. 1.5 for 90 min

Electricity Rate ($/kWh) optional — for cost estimate

Result

Enter values and press Calculate

Formula

Energy Formula

kWh = (W × h) / 1000

Watt-Hours

Wh = W × h

Cost Estimate

Cost = kWh × rate

Result copied!

Summary

Enter power in watts and duration in hours to instantly calculate energy consumption in kilowatt-hours (kWh).

How it works

Enter the power draw of the device in watts (W).
Enter the duration the device runs in hours (h).
Optionally enter your electricity rate in $/kWh for a cost estimate.
Press Calculate to see energy in kilowatt-hours, watt-hours, and cost.
The breakdown panel shows every intermediate value and the applied formula.
Press Reset to clear all fields and start a new calculation.

Use cases

Estimate how much electricity an appliance uses over a day, week, or month.
Calculate the running cost of a heater, air conditioner, or dryer.
Size a solar panel or battery backup system based on daily kWh load.
Compare energy consumption of different devices to find savings.
Verify electricity bill line items against metered watt readings.
Determine generator fuel requirements by converting watt load to kWh output.
Plan EV home charging costs from charger wattage and session duration.
Benchmark data-center or server room power usage in kWh per day.

Frequently Asked Questions

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Last updated: 2026-05-23 · Reviewed by Nham Vu