Capacity concept

Description
At the Booking Calendar Business Large (old Hotel Edition) and MultiUser versions are possible to set the capacity of the booking resources. It's mean that visitors of your site can make several bookings per same selected FULL (not a time slot) date in specific calendar (booking resource). It's usefull if you are have several rooms of the same type or several seats for some place or any other service or properties, where is need to have possibility to book several times for the same date. So at these versions are possible to set capacity of the booking resource, so date(s) in calendar will be available until number of reservations is less then capacity of the booking resource; but in these versions are possible to make reservation only for FULL date, not a time slots (time slots in this version only record data in DB, but not play any logic in reservation) for the booking resources with specific capacity.
Configuration
If you are need to configure the booking resource(s) with some capacity, so you are need to add the "child" resources to your "parent" resource at the top form of Booking > Resources admin page. 
Just create one resource, and then create several child resources (set parent resource for them as a first resource), so the capacity of the first resource will increase.
Capacity it's number of times, which is possible to reserve the same date in calendar, based on number of selected visitors in the booking form. Resource its more like room, where is possible to be several seats for the visitors. 

Here is examples of different configuration of capacity settings.

The availability (number of seats/maximum amount of people ) can be calculated only based on the "visitors" shortcode (shortcode

[select visitors "1" "2" "3" "4" "5"]
in the Booking > Settings > Fields page at top form ). Its can not calculate availability based on the adults or children shortcodes.

You need to activate "Set capacity based on number of visitors" option at the general booking settings page at advanced section. After that you will see the maximum number of visitors at the Resources page.

Also you can read more here: http://wpbookingcalendar.com/help/booking-resource/

Let say you are having booking resources like this:

test   (parent resource, capacity = 3)   Max. visitors = 2
- test 1
- test 2

A) If you are do not activate the "Set capacity based on number of visitors" so then, during reservation process you will book only ONE available booking resource, do not depend from the any number of visitors selections in the "visitors" select box. So it's mean if you are select 1 or 2 or 5 visitors in the select box at the booking form, you will reserve only one booking resource (firstly its will be parent resource "test", during the next new (second) reservation it's will be child resource "test 1" and during third reservation you will reserve "test 2" booking resource.
If the "Set capacity based on number of visitors" is not checked, the availability for the specific date will be 3 (based on capacity only) and during reservation process the selection number of visitors will not impact to the Availability and just will be saved as a any other field.

B) If you will set checked the "Set capacity based on number of visitors" option and activate first radio button in sub settings:

Add tooltip on calendar(s) to show availability based on the number of available booking resource items remaining for each day.
Note: Be sure to match the maximum number of visitors for the one booking resource with the number of visitors specified on the booking form.

Then the Availability in the mouse over tool-tip will be based on the capacity of the booking resource. So it's mean that for the free dates the availability will be show as 3, as in our previous example.

But during reservation process, you can not select more than 2 visitors in the select box. Because each booking resource, is support only 2 visitors per resource.

In other words, during reservation process you can reserve only 1 booking resource during one reservation, but the system is also check that the number of visitors, which you are selected in the booking form have to be not more then maximum number of visitors, which you are set at the Booking > Resource page. The availability in mouse over tooltip will be based on the capacity and in out example will be show as 3

C) And now last variant, if you had selected the bottom radios button option:

Display tooltip on calendar(s) to show availability based on total (fixed) number of visitors for the resource, which can be at free booking resource items.
Note: Be sure to match the maximum number of visitors for all booking resources with the number of visitors specified on the booking form.

So it's mean that availability over the specific date will be based on the capacity and number of maximum visitors per resource. In our example it's will be show as 6 ( 3 * 2 = 6 ).
During reservation process the system can book several booking resources, it's will calculate the visitors, which you are select in the booking form for the each booking resource (parent or child) and number of visitors per this resource.

So for example if you are select 3 visitors in the booking form. It's will reserve 2 booking resources. Because first resource is support 2 visitors and second is support also 2 but we are have only 1 ( 3 - 2 = 1 ), in other words one bed will be free in the second resource.

How all this capacity concept is working for search availability in search form at front-end side ?

You can test search form in action at the live demo of Booking Calendar Business Large version.

During searching availability in search form, number of selected visitors (shortcode [search_visitors] in the search form at Booking > Settings > Search page), can work in several ways. It's depend from selected or do not selected option: "Set capacity based on number of visitors" at the General Booking Settings page in advanced section and selected additional parameters.

A) If "Set capacity based on number of visitors" option UNCHECKED (not selected), then search availability form will search for available booking resources only based on the Check In/Out dates and possible some other parameters, but its will not depend from the selected number of visitors.

You can select any number of visitors and its will show items in search results, if other parameters (check in/out dates and possible some other parameters fit to selected options in search form).

B) If "Set capacity based on number of visitors" option CHECKED and you activated this sub option:

Add tooltip on calendar(s) to show availability based on the number of available booking resource items remaining for each day.
Note: Be sure to match the maximum number of visitors for the one booking resource with the number of visitors specified on the booking form.

Then during search process, the number of visitors (selected in the search form) must be equal or less then maximum number of visitors per booking resources (that you set at the Booking > Resources page). Its does not depend from the number of available "child booking resources", if the booking resource was configured with specific capacity (have child booking resources) and this booking resources (or at least one child booking resource) have available dates that you are searching.

C) If "Set capacity based on number of visitors" option CHECKED and you activated this sub option:

Display tooltip on calendar(s) to show availability based on total (fixed) number of visitors for the resource, which can be at free booking resource items.
Note: Be sure to match the maximum number of visitors for all booking resources with the number of visitors specified on the booking form.

Then during search process, the number of visitors (selected in the search form) must match the maximum number of visitors for all booking resource. Its means that availability per booking resource calculated as number of maximum visitors per resource multiply on capacity of booking resources (number of child booking resources). If we are having booking resource with capacity 3 (2 child booking resources), and maximum number of visitors as 2. Then maximum availability = 2 * 3 = 6 And its means that, if we selected 6 visitors in the search form we fit to get this booking resource in search results. If we select more than 6 visitors, then we do not match this criteria and this booking resource will not show in the search results.