Formulas in plain sight
Each calculator explains the maths it does below it, with an example you can repeat by hand. We use basic physics (power, energy, time) and the methods published by official agencies such as the U.S. Department of Energy.
Typical values, not your home’s
So you don’t start from a blank page, the calculators come with typical wattages and hours of use, taken from tables published by energy agencies. They’re a guide: your appliance’s real wattage is on its label, and it’s best to use yours.
What we check
- That the Spanish and English versions give exactly the same result: both run the same program.
- That the figures in our articles match what the calculator gives with the same inputs.
- That every fact that isn’t a calculation has a source we have opened and read, and that we say which country and year it’s from.
The limits
Results are estimates. Your actual bill also depends on fixed charges, taxes and tiered or time-of-use rates. A calculator is no substitute for an electrician’s visit or an installer’s survey for a solar system.
Your data
All the maths runs on your own phone or computer. We don’t ask you to sign up and we don’t store what you type into the calculators.