A familiar challenge is working with dB from a series of overall values, e.g. time logged LAeq or 1/3-octave spectrum, is you cannot arithmetically sum or average them.
The classic formula involves converting each cell from dB to Pa, summing the Pascal, and convert back to dB
Both Microsoft Excel and Google Sheets have an easier method, Array Formulas.
In MS Excel the below is equivalent
“This is an array formula, so it must be entered with Ctrl+Shift+Enter.” http://www.mrexcel.com/archive/Formulas/4130.html
In Google Sheets the formula is similia
Besides SUM(), other function like =AVERAGE() can be used on arrays