J-Rat Engineering Tools is a collection of free practical calculators and utilities for electronics, ESP32, LoRa, Home Assistant and DIY projects. The aim is to make the calculations that sit behind a build easier to understand without turning them into a spreadsheet exercise.

Available tools

ESP32 Battery Life Calculator

Estimate how long your ESP32 project could run from a battery without needing to know the current draw first. Choose your board and project type for a quick planning estimate, use measured values when your build is ready, or work backwards to estimate the battery size you need.

Solar & Battery Sizing Calculator for ESP32 Projects

Size a battery and solar panel for an ESP32, LoRa node or other DIY sensor from its daily power use. Check cloudy-day reserve, solar headroom and how quickly the battery could recover after poor weather.