FermiFriend is a web-based math tool designed to teach students essential estimation skills through engaging back-of-the-envelope calculations (aka Fermi problems.) With its simple, fun interface, FermiFriend empowers students of all ages to explore real-world questions by posing their own estimation challenges. The tool provides helpful scaffolding to guide students through the process, encouraging critical thinking and fostering an intuitive understanding of order-of-magnitude calculations. FermiFriend makes estimation accessible, interactive, and enjoyable for all math learners.