This tool makes it easy to calculate gear ratios and speeds attainable for all of your bicycle gear combinations at once, whether you're an experienced bike builder or a first time bike hacker. It has been built to allow you to easily iterate your gear setup, and easily compare different gear setups too. If you are new to it and don't know what it does, just follow the prompts at the beginning (you might need to refresh the page).
Inspiration for this came whilst using the calculator Sheldon Brown built but finding it complicated and inconvenient to use. Extra features are being added to this all the time. If we're missing something you want, let us know!