If you are using the NewRelic add-on you can go to the "dynos" tab and see the memory footprint of your application over time. The Heroku memory cap is 512mb,

If you are using the NewRelic add-on you can go to the "dynos" tab and see the memory footprint of your application over time. The Heroku memory cap is 512mb, so if you stay a decent amount of space clear of that then you are likely to be ok running multiple workers per dyno. For instance, our app which I'd say is a medium sized rails app, generally consumes between 175mb and 210mb of memory. So we /should/ be safe running 2 workers per dyno which would effectively double our processing power. HOWEVER, if you hover over the memory graph it'll tell you the min/max/avg consumption over that particular time period. Looking at that I see we sometimes spike the max over 350mb. The question is, what is that spike going to look like running unicorn. Unfortunately, I can't think of many ways to accurately test/predict that without simply giving it a try. One other thing that was mentioned in the comments of the article is that you can set the unicorn backlog to a very low number (default appears to be 1024) which will apparently tell the heroku router that a particular dyno is "full" and to look somewhere else to process the request. One comment recommends setting the backlog to 25. I wonder what setting the backlog to something like #workers*2 would do.