# How do I calculate the log-average in Excel?

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Hello Forum!

Since the patch I want to know the thermal conductivity between two objects!

I saw the expression referenced in the 266340 update post and applied it in Excel.

Yes they are, see here :https://en.wikipedia.org/wiki/Geometric_mean#Log-average

Did you read my post ? Log-average of a and b is exp((log(a)+log(b))/2 and this is the same thing as the square root of ab.

You are right about that. Since thermal resistance roughly is length/thermal conductivity, and if we take the length to be half the length of the tile (after all this is not a transfer between two extremities of the tiles), then you get the harmonic mean of thermal conductivities.

The thing is, we are not strictly speaking in a case where thermal transfer are ruled by thermal resistance, so I don't know if LMTD is better than harmonic mean.

 Hydrogen Abyssalite Log-Average Square Root 2.4 0.00001 0.099271736 0.004898979 =EXP((LOG(B11)+LOG(C11))/2) =SQRT(B11*C11)

Please let me know if you have any mistakes!

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Use ln (logarithmus naturalis) instead of log then you'll get the same result as the square root of the product of the two

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sqrt(exp(ln(A)+ln(B))/2) = sqrt((A*B)/2)