The debate of whether surface area or volume is the better indicator of size is discussed in this thread
I think surface area is a better measurement than volume.
To quote myself from that thread:
Originally Posted by mravg
volume measurement overstates the growth increase by measuring what is below the surface, which isn’t important. In other words, if you were going to stick a beer bottle into a woman, it wouldn’t matter if the bottle was full or empty, it is only the outer surface she feels.
If you grow from 6x4.5 to 6x5.5, your volume increase is 50% while your surface area increases 22%. Intuitively, I think you would say that the difference between these 2 dicks visually, would be closer to 20% and NOT that the 6x5.5 is 50% more dick than the 6x4.5.
The problem with volume in my opinion is that it overemphasizes girth compared to length, because in the volume formula is V=pi*R squared* L, so that an increase in length would result in a proportional increase in volume, but an increase in girth results in an exponential increase in volume, proportional to the radius SQUARED. So small changes in girth make big changes in volume. The formula for surface area is: A=2*pi*R*L, so that volume goes up the same amount for the same incremental increase in either length or girth.
That is my opinion, but I know a lot of guys like the volume measurement. I think they like it, in part, because they can say things like “I doubled my volume!”, but to me doubling volume does not mean your dick is twice as big.