Enter your data in one column
Calculate the sample mean with `=AVERAGE(range)`
Calculate the sample standard deviation with `=STDEV.S(range)`
Calculate the sample size with `=COUNT(range)`
Choose the confidence level, such as 95%
Find the critical value with `=T.INV.2T(1-confidence_level, sample_size-1)` for a t-based interval
Calculate the margin of error with `=critical_value*sample_stdev/SQRT(sample_size)`
Calculate the lower limit with `=sample_mean-margin_of_error`
Calculate the upper limit with `=sample_mean+margin_of_error`
Use `=CONFIDENCE.T(alpha, standard_dev, size)` to get the margin of error directly for a t-based interval
Use `=CONFIDENCE.NORM(alpha, standard_dev, size)` for a normal-based interval
For a built-in tool, enable the Analysis ToolPak
Go to `Data` > `Data Analysis` > `Descriptive Statistics`
Select your input range and check `Summary statistics`
Review the output for the confidence level value