Ability point

The ability point (AP) is a unit of measurement used internally by Splatoon and Splatoon 2. It measures the amout of ability power used by the player and is defined by the following:

Where:
 * : the number of Ability Points
 * : the number of primary abilities equipped
 * : the number of secondary abilities equipped

History
The ability point measurement is consistent between Splatoon and Splatoon 2.

To date, no Splatoon game has informed players of the worth of the large and small ability slots, with manuals and character dialogue containing only vague information. However, on 2019-02-28 Nintendo published an article on the Nintendo Switch news feed that officially confirmed the value of the large and small ability slots relative to each other.

Example
Since there are a maximum of 3 primary ability slots and 9 secondary ability slots, the maximum number of ability points a player can have is 57, except when using some abilities such as Last-Ditch Effort and Opening Gambit which allow players to have even more ability points (while the relevant conditions are met).

Ability Doubler
Ability Doubler doubles the number of ability points provided by the 3 secondary ability slots on the Splatfest Tee. Since 1 secondary ability is worth 3 AP, Ability Doubler can provide up to 18 AP.