This is from a page I was reading when looking in to maf v injector flow rate.
"Stock 2.5" MAF = about 2.4" at the sensor, radius = 1.2"
New 3" MAF = about 2.8" at the sensor, radius = 1.4"
So, the area increase is:
[1.4*1.4] / [1.2*1.2]
1.96 / 1.44 = 1.36