Prim Count vs Land Impact - confused!

[Carmsie Melodie]

Hi there,

I am very confused about Land Impact (LI). In the following link you'll see an item for sale on Marketplace that has a prim count of 1 but an LI of 40, as outlined in the product description. https://marketplace.secondlife.com/p/MOST-POPULAR-Realistic-Horror-Girl/3931289

What happens if I use this in a build or place it on my land? Will it suck up 1 prim or 40 prims? What's the difference? Can anyone give me a simple explanation?

Thanks :) 

[Lindal Kidd]

To add to Rolig's excellent answer...

In the old days (about three months ago), prim count was prim count.  How many prims you had on your land had exactly the same impact on your prim allowance, whether those prims were plywood cubes, sculpties, or cut and twisted toruses, and regardless of their physics type or whether they contained scripts.

This turns out not to be the best way to evaluate the stress an object puts on the region server.  When Linden Lab introduced Mesh objects, they also took the opportunity to revise the way SL calculates the impact that objects have on the server.  Now, the detail level in a Mesh object, the physics type of the object, its size, and how complex the prims of the object are, all are involved in calculating the object's Land Impact value.

There are articles and formulas that you can look up to find out just how this works (and if you are a creator, you should.)  But for most of us, it's a lot simpler than that.  Land Impact is now the number you have to keep track of when shopping for items to put on your land.  One may also think of this figure by a name it was called by during the beta test period of Mesh...Prim Equivalent Value.  An object with a LI of 40 is the equivalent of 40 prims.

[Rolig Loon]

Calculating Land Impact is a challenge for creators.  For consumers, however, the results are simple.  When you are trying to figure out the effect on your land's total prim allowance, Land Impact means the same thing as prim count.  That is, if you have an object with a Land Impact of 40, and you are allowed 117 prims on your 512 sq m parcel, the object will eat up 40 of that total, leaving you with 77.  It's exactly the same effect as rezzing 40 prims.