Baffle box / Math question

[gullfo]

so, if you have 260cfm and use a 1ft2 duct (round or square) barring all kinds of things like friction etc - you get a speed of about 260fpm velocity. if i go to a 2ft2 duct, i approximately halve the velocity.

12" x 24" = 288in2
20" round = 314.6in2
etc

math (e.g. with inches) (handy sites: https://areacalculators.com/ https://www.omnicalculator.com/)

-> square or rectangular - multiple the height and width = square area

-> round - diameter / 2 = radius, radius^2 * pi = round area.
to get to the diameter = divide by pi (this is radius squared), then squareroot of radius number * 2 = diameter.
e.g. 300in2 = /pi = 95.49 sqrt = 9.77 * 2 = 19.5in diameter

-> ovals are a different equation. https://areacalculators.com/oval-area-calculator/