Knowing how long to develop film for is easy if you use popular films and developers, but what if you want to use some obscure combination that isn’t well documented? If that’s you, check out the Photocritic Film Development Database. It’s a simple service that outputs development times for 1440 different film/developer combinations. For combinations that aren’t officially published, creator Haje Jan Kamps has come with a formula that estimates the time — a formula that he says is surprisingly accurate.
Update: Digitaltruth also has a massive film development database/chart.