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Work · August 17, 2022

I made a web-based notepad with a built in unit calculator

I launched NumPad v1 on here a few years ago, and back then it wasn't much more than a thin CodeMirror wrapper around the calculator engine I'd written. Now I've rewritten it as a PWA that supports multiple documents, persists them to IndexedDB, and has a syncing service for paying customers. Syncing is handled by Automerge[1] under the hood, which should make it relatively easy to get document sharing working too. [1] https://automerge.org/

I made a web-based notepad with a built in unit calculator launched on August 17, 2022 with 488 votes, #19 of 3,307 launches that month and more than 99% of that year's launches. The site was still online in September 2026, 4 years on.

Visit numpad.io ↗Alternativestop 1% of August 2022

In plain words

This is a web-based notepad that combines note-taking with built-in unit calculations. It supports percentages, dates, and variables alongside standard mathematical operations. The tool is designed for anyone who needs to perform calculations while taking notes, eliminating the need to switch between applications. The creator has spent several years developing this single-person project.

written from the facts on this page · September 2026

From the sources

NumPad is a fast, lightweight web app with support for units, dates and more. It lets you keep notes and calculations in one document, gives you answers as you type, and it understands calculations like "£200 + 20%" or "2500kcal / 1 day in watts".

A powerful calculator and text editor rolled into one

In the maker’s words, at launch

Hi HN It also supports percentages, dates and variables. I've been working on this alone for a few years now, so would love to get some feedback.

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