Significant digits of a number are the digits which contribute to its accuracy - generally these are all digits except leading and trailing zeros. For a more precise definition please see WolframMathworld.
An Excel © worksheet function solution to calculate n significant digits of d (I found this in an Excel forum but I could not identify the original author): A1: d A2: n Result: =--TEXT(A1,"."&REPT("0",A2)&"E+0")
Example: If you want to show pi with 3 significant digits:
The corresponding VBA solution:
Function sbNSig(d As Double, n As Long) As Double
'Returns double with n most significant digits of d.
'09-Nov-2019 by www.sulprobil.com PB V1.00
sbNSig = Format(d, "." & String(n, "0") & "E+0")
Klaus K. offered another worksheet formula for this on the (retired) web site www.Excelformeln.de: =ROUND(A1,A2-1-INT(LOG(ABS(A1))))