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Pizza Rule
(telegra.ph)
Be sure to follow the rule before you head out.
Rule: You must post before you leave.
You can compare areas with just r^2 you don't even need pi. So the math is easy.
A pizza is larger than two of another just before it hits 1.5 times the radius (sqrt 2 times, to be exact, about 1.41). So if the radius is 1.5 times bigger, like in the OP, you always know it's more than twice the area.