Kilowatt hour
A watt (W) is a unit of electrical power. One watt represents a current of one ampere with a voltage of one volt.
A kilowatt hour (kWh or kW h) is a unit of energy that is equivalent to 1,000 watts (1 kW) of energy being transmitted or used for one hour. The kilowatt hour is commonly used by utility companies for pricing, calculating and communicating electricity energy bills to consumers.
One kilowatt hour is equal to 3.6 megajoules – the amount of converted energy if work is done at an average rate of 1 kW per hour.
The difference between a kW and a kWh is that a kW is the energy required for an appliance to function, whereas a kWh is the amount of energy that is actually used over a period of time.
For example, a 100 W light bulb would take 10 hours to consume 1 kWh of energy. A 50 W electrical appliance that is used at a constant rate for 20 hours would use 1 kWh of energy. A 2 kW electrical appliance would use 1 kWh in 30 minutes.
To calculate the cost of running an electrical appliance, the power consumption in kWh is multiplied by the price per kWh. The unit price of electricity often varies depending on the rate of consumption, the time of day, and the location.
[edit] Related articles on Designing Buildings Wiki
- Ampere.
- Conductor.
- Domestic micro-generation.
- Electricity.
- Energy.
- Glossary of electrical terms.
- Portable Appliance Testing (PAT).
- Power.
- Power generation.
- Smart meter.
- The future of electricity in domestic buildings, a review.
- The UK’s low-carbon future is increasingly electric.
- Voltage.
- Watt.
Featured articles and news
Licensing construction in the UK
As the latest report and proposal to licence builders reaches Parliament.
Building Safety Alliance golden thread guidance
Extensive excel checklist of information with guidance document freely accessible.
Fair Payment Code and other payment initiatives
For fair and late payments, need to work together to add value.
Pre-planning delivery programmes and delay penalties
Proposed for housebuilders in government reform: Speeding Up Build Out.
High street health: converting a building for healthcare uses
The benefits of health centres acting as new anchor sites in the high street.
The Remarkable Pinwill Sisters: from ‘lady woodcarvers’ to professionals. Book review.
Skills gap and investment returns on apprenticeships
ECA welcomes new reports from JTL Training and The Electrotechnical Skills Partnership.
Committee report criticises UK retrofit schemes
CIOB responds to UK’s Energy Security and Net Zero Committee report.
Design and construction industry podcasts
Professional development, practice, the pandemic, platforms and podcasts. Have we missed anything?
C20 Society; Buildings at Risk List 2025
10 more buildings published with updates on the past decade of buildings featured.
Boiler Upgrade Scheme and certifications consultation
Summary of government consultation, closing 11 June 2025.
Deputy editor of AT, Tim Fraser, discusses the newly formed society with its current chair, Chris Halligan MCIAT.
Barratt Lo-E passivhaus standard homes planned enmasse
With an initial 728 Lo-E homes across two sites and many more planned for the future.
Government urged to uphold Warm Homes commitment
ECA and industry bodies write to Government concerning its 13.2 billion Warm Homes manifesto commitment.
From project managers to rising stars, sustainability pioneers and more.
Places of Worship in Britain and Ireland, 1929-1990. Book review.