Formula for Buckling Load

The problem:
This problem was originally multiple choice, but now all of the answers except for the one I chose are hidden.
To analyze the buckling load for slender columns, the Euler’s equation is used: Fb = (n * π^2 * E * A) / (L / r)^2 where :
Fb =Buckling Load, lbs E = modulus of elasticity, 3.00E+07 lb/square in
A = cross sectional area, 7.33 square inches L = length of column, inches
r = least radius of gyration, 3.19 inches n = 4 if both ends are fixed
Using the information above & the sample Excel Spreadsheet below, select the input formula that would be needed for calculating the Buckling Load in pounds using cell locations and a beam length of 25 feet from one of the following answers shown below:
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My answer
=(B7*pi()^2*B3*B4)/(B6/B5)^2

This was incorrect, but I can't figure out why. All of the answers looked pretty similar. What do you think I did wrong?

Originally Posted by martindwilson

beam length of 25 feet =25*12 =300 maybe

Can you explain a little further?

Oh. I see. I need to convert the Length to inches. Sooo:
=(B7*pi()^2*B3*B4)/((B6*12)/B5)^2
Am I missing anything else?

Yeah, after working it out on paper and canceling out units, I ended up with lbs like I was supposed to so I think that was all I was missing. You rock, martindwilson.

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