Free Tools From One Real Smart Home Build
Calculators I wanted while wiring this house and couldn't find without a signup wall. Each one runs entirely in your browser: no account, no upload, no tracking of what you type. They use your numbers, not somebody's averages, because an average house isn't the one you're paying for.
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Energy
Electricity Cost Calculator
Enter the rate from your bill and the devices in your house. Get cost per day, month, and year in EUR, with the biggest offender sorted to the top.
Why so few?
Because a tool page you build in an afternoon is a toy, and the web has enough of those. Each tool here starts as a spreadsheet I made for an actual decision during the build, and only gets published once the math has unit tests behind it. More are coming as the house generates them. If there's a calculation you keep redoing for your own smart home, tell me on X (Twitter) and it goes on the list.
How the numbers are computed
Every calculator on this page works from the same three rules. First, your inputs stay yours: the math runs in your browser, nothing is sent to a server, and reloading the page wipes it. Second, no averages stand in for measurements. The electricity calculator asks for the rate printed on your bill and the wattage printed on the device label, because a national average kWh price applied to an average household answers a question nobody asked. Third, the formula is stated on the tool page itself, so you can check the arithmetic with a pocket calculator and get the same result.
That last rule exists because this site reviews devices that promise savings, and a promise you cannot verify is marketing. A smart plug that claims to cut standby cost has to beat the math here: watts times hours times your rate, nothing else. When a review on this site says a device pays for itself, the claim was run through the same arithmetic these tools expose.
Want the reasoning behind the numbers instead of just the output? The build log covers the decisions these tools automate.