It really depends on your application. A fresh rails app will take up ~30mb of memory (iirc, been a while since I checked). Thirty gems and 11,000 lines of code later, yes, it can spike to 256mb.
If I were to toss down an average, seems like ~100mb is what I see most of the time for non-trivial rails apps.
The main Rails app that I work in is a medium sized app and runs at 220mb memory usage on a dyno on averae. It spikes to the 350mb range occasionally probably from image generation with rmagick or PDF generation.
If I were to toss down an average, seems like ~100mb is what I see most of the time for non-trivial rails apps.