Power & electrical calculators
Precise, free tools for wire sizing, voltage drop, batteries, solar, and backup power.
Electrical
Look up AWG conductor diameter and cross-sectional area, 4/0 to 30 AWG.
Inverter Size Calculator
Size an inverter from your continuous load and largest single starting surge.
Battery Runtime Calculator
Estimate how long a battery will run a given load, from capacity, voltage, and depth of discharge.
Solar System Size Calculator
Estimate the solar array size and panel count needed to offset your daily energy use, from your own peak sun hours and system losses.
Generator Size Calculator
Calculate what size generator you need from your appliance list — running load, worst-case starting surge, and a suggested size.
kVA to kW Calculator
Convert between apparent power (kVA) and real power (kW) using your equipment's actual power factor.
Every calculator, grouped by the kind of problem it solves.
Clear formulas, explicit assumptions, and practical tools. No signup required.
Clear formulas
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Explicit assumptions
Required inputs are clearly identified. We don't invent values just to make a result appear.
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Most calculator sites either hide their math behind a black-box "result" box or fill the page with generic content written to rank rather than to help. FigureDesk takes a different approach: every calculator shows the exact formula and substitution it used to get your number, so you can check it yourself instead of trusting it blindly.
Where a result depends on a value only you know — a battery's depth of discharge, an inverter's rated efficiency, a panel's real-world derate — the calculator asks you for it directly instead of quietly assuming a default. A guessed default that happens to be wrong is worse than a form that asks one more question, especially when the answer feeds into sizing hardware you're about to buy.
FigureDesk is built and maintained by one person, not a company, and every result is advisory rather than a substitute for a licensed electrician, a qualified engineer, or your local electrical code — see About for more on how the calculators are built and sourced.