The standard Lr licence allows for two installations on different computers, as long as both are not used at the same time by different people.
So, if only you are using these computers, then you would need 3 licences at first glance. However, if a combination of different people were using them, then it gets more complicated. And more licences would be necessary.
Perhaps you could tell us how these computers are to be used, and how many people are involved.
We have 3 photographers that each need Lightroom 5 on their computers. They will all be using Lightroom 5 at the same time.
If possible, the photographers would like to use Lightroom on one laptop and one iPad.
If not, the main thing we need is Lightroom 5 for 3 photographers, on 3 different computers. Thanks!
Okay, that clears things up, but at the risk of telling you something you already know, you would have to use the CC version of Lr, as perpetual licences don't work with Lr mobile as used on the iPad.
If each photographer is using one laptop and one desktop, with Lr mobile, then one licence in each case will cover that, making a total of three licences.
Hope that helps.