spread of round vs princess cut

[mbn]

I got this from this forum:

Romeo you can compare the spread of a princess cut to a round diamond by this arithetic -
Spread of princess cut = LXW
Spread of round diamond = 1/2 diameter x 1/2 diameter x 3.142
Expect lucida / radiant / princess will have much smaller spread.


If I compare spread of a 1.5 carat 6.5x6.5 princess cut = 42.25
to spread of a typical 1.5 carat round 1/2(7.5) x 1/2(7.5) x 4.142 = 44

So princess cut spread is smaller, but is it that much smaller given the above parameter?

 

[Garry H (Cut Nut)]

Yes - because the princess is also very flat whereas you can see a lot more crown on a round.
The brilliance of a well cut round also makes it appear another 10% or so bigger too!