SMPS Transformer Area of Product
Now that we've got the formula and source reference we can see that the source mentions on page 8 the area product which is different to the &quot;area of product&quot; in your question. (If you want an &quot;of&quot; in there it would be the &quot;product of areas&quot; rather than the other way around.)

Core Selection: Size
A novice in the art of transformer design usually
needs some guidance in making an initial estimate of
the core size appropriate for the application requirements. One widely used method, with many variations, is based on the core Area Product, obtained by
multiplying the core magnetic cross-section area by
the window area available for the winding.

Just before the AP equation the article explains ...

Some core manufacturers no longer provide area
product information on their data sheets, often substituting their own methodology to make an initial
core size choice for various applications.

That means that you'd have to calculate it from the information given in a datasheet.


Going back to the datasheet we can see that the area of the centre core, AE is 20 × 27.4 = 540 mm2 = 5.4 cm2.
I don't know whether the winding window is in the same orientation or at right angles so I'll assume that it's in the same plane as AE. From the drawing we can calculate that the window area, AW = 12 × 27.4 = 324 mm2 = 3.24 cm2.
AW (often referred to as AN in datasheets) is the area that is filled by the cross sections of the wires:

AW = (22.2 × 2) × (12) = 533mm² = 5.33cm².
Since some of this area is occupied by the bobbin (a.k.a. coil former), it's always lower than calculated. That's why this area is given in the datasheets for various types of bobbins for the same core. As can be seen at p.4 in the datasheet, AW is given as 4.35cm² for the only bobbin. As stated above, winding window area is mostly given as AN in datasheets.
From those numbers we can calculate:
AP = AE × AW = 5.4 × 3.24 = 17.5 cm4 5.4 × 4.35 = 23.5cm4
Remember that I don't know what I'm talking about.