Built by energy professionals. Designed for everyone.
Free, no-signup energy calculators—from AI data centers to everyday home energy costs. Every calculation explained. Every source cited.
Residential Energy
For homeowners, renters, contractors, electricians, and residential solar installers — practical answers without requiring an engineering background.
Commercial & Industrial
For facility managers, business owners, consultants, EPCs, and energy professionals quantifying savings, operational improvements, and resilience.
Battery Energy Storage (BESS)
One of the fastest-growing sectors in energy and a signature WattThe?! content area — tools for beginners and experienced professionals, residential through utility scale.
Solar Energy
For homeowners, developers, EPCs, engineers, and investors — technical performance and project economics with irradiance, degradation, and loss assumptions shown.
Wind Energy
For developers, consultants, utilities, and students evaluating project feasibility and production.
Calculators coming soon — view the roadmap.
Hydrogen
For engineers, project developers, policymakers, and investors exploring emerging hydrogen technologies.
Calculators coming soon — view the roadmap.
Electric Vehicles
For consumers, fleet managers, charging network developers, and utilities.
AI & Data Centers
Data centers are among the fastest-growing electricity consumers in the world — tools for developers, investors, operators, and utilities to estimate demand, infrastructure sizing, operating costs, and sustainability impacts.
Utilities & Grid Operations
For utilities, system operators, consultants, and engineers working on transmission, distribution, and grid planning.
Calculators coming soon — view the roadmap.
Financial Analysis
Consistent methodologies for evaluating energy investments across technologies and project sizes — assumptions, discount rates, escalation, financing, and tax considerations documented.
Calculators coming soon — view the roadmap.
Units of electricity
Power and energy are different things, and the difference is the key to every calculator on this site: power (watts) is how fast electricity is being used right now, while energy (watt-hours) is how much has been used over time. Utilities bill for energy, so cost is always wattage × hours — never wattage alone.
A watt (W) is the base unit. A kilowatt (kW) is 1,000 watts, and a kilowatt-hour (kWh) is one kilowatt sustained for one hour; it is the billing unit because a typical US home uses ~10 million watt-hours a year — 10,000 kWh reads better.
A megawatt (MW) is 1,000 kilowatts — one million watts — and a megawatt-hour (MWh) is that power sustained for one hour. These are the working units of data center developers and utility-scale energy projects: an AI campus is negotiated in MW of grid capacity, a solar plant is nameplated in MW, and battery storage is bought and sold in MWh.
The BTU (British Thermal Unit) measures heat: 1 kWh equals 3,412 BTU. It's how an air conditioner's rating connects to its electrical draw, and how a data center's IT load becomes a cooling problem.
Horsepower is 745.7 W (mechanical) or 735.5 W (metric), thanks to James Watt, who invented the unit to sell steam engines against draft horses — rounded, one horsepower is 746 watts.
And the ton of cooling — 12,000 BTU per hour — is sized for everything from a home AC to a data center chiller plant. One ton of cooling typically requires about 1–1.2 kW of electricity.
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