Is it possible to know how much the cake weighs using a specific size of cake pan before baking?

It is a question of scaling.

• In chat you told us the given recipe was for a 23 cm pan.
• I'll ignore height for now, assuming the same height for all pan sizes, because that can be adjusted in a second step.

The math:

• The cake batter for round cakes fills a cylinder.
• The volume of which is base circle area x height, ignore height as stated above.
• The formula of a circle is pi x r². As pi is constant, ignore it.
• So for scaling, you only need to look at the radius (1/2 diameter) of the pans - or even the diameters.

Divide the desired diameter (or radius) by the original one and square the result.

-> Use that value to multiply all ingredients.

Further adjustments:

Height scales linear - for a cake that is 1.5 times as high as the original, you need 1.5 times the batter etc.

So for your question:

To go from a 23cm / 9in cake to a 28cm / 11in cake,
you need (28/23)² = 1.48 times the original recipe.

My personal gut feeling: three of those won't feed 100-150 guests.

An experienced cake baker friend of mine suggests one egg per five guests when making sponge wedding cakes like chocolate or vanilla (not traditional Buritsh fruit cakes, which is the norm where I come from)

I'm in the same boat, of cooking my first wedding cake for 150 guests, and I'll be making a 30-egg cake on that basis.

You are asking about weight. A cake pretty much weighs the same as the sum of its ingredients (maybe some slightly evaporation from the buttermilk). There are plenty of free cup to gram converters on the internet, just use one of those to get an idea how close you are to your 4 kg goal. An egg weighs about 60 - 80 g, but it depends on the size.

So, here's is what I did:

I did calculate the volume of the cake pan I wanted to use (37 x 5 cm) and the one the recipe calls for (23 x 4 cm), thanks to @Stephie's answer. From the ratio, I figured how much batter is needed to fill the 37 cm cake pan. As for the baking of the large cake, I did take @Joe's advice, used an old towel and a tin can opened from both sides in place of flower nail. The other point @Joe mentioned was longer baking time in lower temperature, I usually bake the cake of the original recipe for 35 minutes in 180 C so I reduced the temperature to 150 and baked the large cake for 50-55 minutes. It turned out just like the small cakes.