truncated cone volume formula in excel

[savagear]

Hi,

I tried to write formula for calculating volume of truncated cone. I see that there is something wrong because web calculators get diferent answer.What is wrong in my formula? My file is attached.

Thank you in advance,
Andrus from Estonia

[MrShorty]

Are you using the correct formula for the volume of a truncated cone? Your formula in D2 does not look the same as the formulas derived here: https://mathemaphilia.com/unit/volume-truncated-cone/ When I use mathempahilia's formula, I get 0.2978..., which rounds down to 0.29 that you show for the Web result.

[curiouscat408]

What is wrong in my formula?

Your formula: =ROUNDUP(1/3*PI()*A2 *B2^2+C2*C2^2+B2,2)

Your mistakes:

1. You are missing parentheses around the expression B2^2 + C2*C2^2 + B2 (sic)
2. The correct expression is B2^2 + B2*C2 + C2^2
3. You(?) truncated the online calculator result -- or it did. The online calculator that I found returns 0.2978
4. You round up the result. It is usually more appropriate to simply round

The following image demonstrates the correct calculations (in green). See the attached Excel file for details.

trunc cone xl.jpg
D3: =ROUND(1/3 * PI() * A2 *(B2^2 + B2*C2 + C2^2),4)

trunc cone calc.jpg

PS.... __I__ did not enter the "slant height" field. The online calculator did that automagically. I have no idea what that is; and I don't care. It has no bearing on this calculation. (Well, I did not find it with a google search.)

PPS.... For clarity, I would reorder the terms and write:
PI() * A2 *(B2^2 + B2*C2 + C2^2) / 3

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