Electrical & Off-Grid Power Calculators
Free, no-signup calculators for wire sizing, voltage drop, ampacity, conduit fill, Ohm's law and breaker size — plus solar arrays, battery banks, inverters, generators, RV 12V wiring and energy cost. Each tool ships with the formula, a worked example, a reference table and a source. Results are estimates for planning and education.
Topics
Tables and guides
- Reference tables — AWG wire chart, NEC ampacity, conduit fill, voltage drop, resistivity, peak sun hours and appliance wattage.
- Guides — the why behind each calculation, step by step.
What you can work out here
WattCalcs is a free, no-signup hub of calculators for electrical and off-grid power work, built for DIYers, electricians, and solar, RV and van builders. Every tool is deterministic: it runs an explicit formula on the values you enter and shows that formula, a worked example, a reference table and a cited source right on the page, so you can check the reasoning rather than trust a black box. Nothing here depends on a price feed or a login — the math is timeless physics and the constants are stable engineering reference data.
The site is organised into six areas. Wire and circuit sizing — voltage drop, wire size, ampacity, conduit fill, Ohm's law and breaker size — is the electrical core, where the answer is whichever of the ampacity and voltage-drop checks demands the larger conductor. Off-grid and solar sizing works from your daily watt-hours out to panels, batteries, inverters and charge controllers. Generators and backup power add up running and starting watts to a generator rating. RV, van and marine power handles the heavy low-voltage DC wiring those builds need. Energy use and cost turns wattage and your own electricity rate into money. And motors, lighting and conversions covers the everyday W/A/V/kVA and three-phase conversions that sit under everything else.
Not sure where to start? Browse the guides for the why behind each calculation, or the reference tables for the AWG chart, NEC ampacity, conduit fill and peak sun hours. Because electrical work is safety-critical, every result is an estimate for planning and education: verify all sizing with a licensed electrician and your authority having jurisdiction against the NEC edition adopted where you live.