Who runs it
Size Your Power is created and published by Fathi Arfaoui.
How each calculator is built
- One question per tool. Each calculator answers a specific question, such as how long a battery lasts or what wire a circuit needs, instead of repeating the same content in different places.
- Formulas on the page. Every page lists its formulas and defaults so you can check them by hand.
- Tested before publishing. The math is covered by automated checks, including edge cases such as empty inputs, and the page is tested in a browser on desktop and mobile layouts.
- Worked examples. The examples and quick answers on each page are produced with the same code as the calculator, so they match what you will see.
- Dated. Each page shows when it was last updated.
Where the numbers come from
- Cable current ratings come from copper values in the US National Electrical Code ampacity table (NEC Table 310.16), with small-conductor limits applied. Metric sizes are matched to the next smaller AWG size, which is conservative.
- Copper resistivity is taken as 0.0175 Ω·mm²/m, a standard value near 25 °C.
- Inverter efficiency (85%), solar system losses (25%), depth of discharge and Peukert exponents are typical values. They are labelled as typical and can be changed where it matters. Your battery’s datasheet is always more accurate.
What the calculators do not do
- They are planning aids, not electrical advice or a code compliance check.
- They do not replace your local rules, such as the NEC, ABYC, ISO 10133, IEC 60364 or AS/NZS 3001.
- They do not cover household AC wiring, gas systems or structural mounting.
- Have a qualified installer check safety-critical work, especially batteries, fuses and inverters.
Contact
Found a mistake in a formula or an example, or want to suggest a calculator? Email contact@sizeyourpower.com. Please include the page address and the numbers you entered, so the result can be checked.
Copyright and use
© 2026 Size Your Power (sizeyourpower.com). The text, tables, calculator code, design and logo on this site are protected by copyright. You are welcome to link to any page and to quote short excerpts with a link back to the source. Please do not copy, republish, scrape or rebuild the pages or calculators without written permission. To ask, use the contact address above.
Some figures come from public sources, such as the U.S. Energy Information Administration and the ampacity values of the US National Electrical Code, and are credited where they are used.
Privacy
The calculators run in your browser and what you enter is not sent to us. See the privacy page for details.