How to limit a number of seats?

Hallo,

I need to know whether is possible the thing like this:

I have a limited number of seats in the room. Every registered person fill the number of people coming with him. It is possible that the different person who is registered himself after that person will see how many chairs are left. 

Sorry for my English, but I am from slovakia. :)  

You can use widgets like the Quantity Gift Registry or Inventory, to limit a number of seats that you have. 

How to Add a Widget to your Form?

Hope this meet what you are looking for.