Using the field Consumer utilisation in the RabbitMQ interface you can get a figure of how many more consumers you can add. Often developers find themselves wondering how well they can scale their applications. Consumer utilisation is great for this and can be found when you look at a queue in the web interface:
Above I currently have zero consumers or no messages. Therefore the utilisation is 0. If rabbit could not keep and I had too many consumers, then this would have been at a 100%. Often you will see this being much lower and RabbitMQ can keep up. So if your utilisation is at 10% with one consumer. Then you should be able to add 10 more consumers. Other than adding more consumers to a queue you can also change the prefetch count for your consumers. This will make them prefetch more and ack them as they are handled.