What does it mean that your web site can handle 50 ‘transactions’ per second? The general rule of thumb is that 1 transaction per second maps to 1000 users based on the following model of user behavior (your results may vary):

• 1000 users
• 10% peak concurrency
• 100 simultaneous users (10% of 1000)
• 100 seconds per request per user (36 requests per hour per user)
• 100 simultaneous users/100 seconds per user per transaction
• 1 transaction/second.

So if your website can handle 50 transactions per second you could assume it could handle 50,000 users. Of course, if your traffic is related to say a television show you could easily expect this model to be wrong. Why? The traffic is queued to your promotion. For example, we host a podcasting application for Nip/Tuck and as soon as the show ends and our promo appears before the commercial we see a huge spike in traffic. Now 1 transaction per second maps to 100 users ~ a 10x decrease in user count.