Scaling down Delia's Creole christmas cake help

[NecklessMumster]

I'm behind this year with making my christmas cake, I usually do the Creole cake but in a 15 cm round tin, as a bigger cake doesn't get eaten. I can't find my previous measurements though, to scale down from her 20 cm recipe. Chat gpt is giving me a different answer from my calculations, although I may be overthinking this. Can anyone help?

So a cake is effectively a short fat column so you can use the volume of a column equation volume =height x pi (~3.14) x radius squared to determine the size difference. That sounds complicated but for a rough and ready version for the purposes of baking a 15cm diameter column has just over half the volume of a 20cm diameter column of the same height so I'd just half the recipe.

Thank you! I did see a mathematical equation for it but was too hard for me! I'll do half then. I think last year's had a bit too much batter so half may be better