How to Calculate Logarithmic Interpolation in Excel (2 Easy Ways)

Interpolation is a process of determining the value of an unknown point that lies between two known data points. While calculating linear interpolation is an easy task in Excel, people often have to struggle when dealing with a non-linear dataset. Logarithmic graphs often convert a non-linear equation into a linear one, making it suitable to interpolate unknown values. In this article, we will show you two easy methods to calculate logarithmic interpolation in Excel effectively, with appropriate illustrations.

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2 Suitable Ways to Calculate Logarithmic Interpolation in Excel

1. Use Mathematical Formula to Calculate Logarithmic Interpolation in Excel

2. Utilize FORECAST Function to Calculate Logarithmic Interpolation in Excel

Conclusion

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2 Suitable Ways to Calculate Logarithmic Interpolation in Excel

In this article, we will demonstrate two suitable ways to calculate logarithmic interpolation in Excel. We will use the following dataset for this purpose.

1. Use Mathematical Formula to Calculate Logarithmic Interpolation in Excel

In this method, we will use a mathematical formula to calculate logarithmic interpolation in Excel. Follow these steps to learn how to do it.

Steps:

First of all, let’s assume, Depth of Flow = X and Discharge = Y.
Then, insert two columns named LogX and LogY.
After that, select cell D5 and write down the following formula.

=LOG10(B5)

Similarly, select cell E5 and type the following formula.

=LOG10(C5)

Hence, Autofill the formula to the rest of columns D and E.

Now we want to calculate the value of Discharge for a 0.175m Depth of Flow.
To do so, select cell D12 and write down the following formula to determine LogX for 0.175m Depth of Flow.

=LOG10(B12)

Then select cell E12 and type the formula given below and hit Enter.

=E7+((E8-E7)/(D8-D7))*(D12-D7)

After that, select cell C12 and write the following formula.

=10^E12

Where E12 is the value of LogY.
Finally, press Enter to get the interpolated Discharge value for 0.175m Depth of Flow.

2. Utilize FORECAST Function to Calculate Logarithmic Interpolation in Excel

In this method, we will use the FORECAST function to determine logarithmic interpolation in Excel. Read the following steps to learn the procedure.

Steps:

First, follow the same steps as the first method up to calculating LogX for a 0.175m Depth of Flow.
Then select cell E12 and write the following formula, given below.

=FORECAST(D12,E5:E9,D5:D9)

After that, select cell C12 and type the following formula.

=10^E12

Finally, hit Enter and get the desired Discharge value for 0.175m Depth of Flow.

Notes

These two methods give good results if the LogY vs LogX graph is linear.
Don’t forget to give proper cell references or you won’t get the desired result.

Conclusion

Thanks for making it this far. I hope you find this article useful. Now you know two methods to calculate logarithmic interpolation in Excel. Please let us know if you have any further queries, and feel free to give us any recommendations in the comment section below.