Rounding to Two Significant Digits

Tammy needs to round values in a worksheet to two significant digits. For instance, if a cell contains 137, it should round to 140; if it contains 0.0005937 it should round to 0.00059; and if it contains 156735.32 it should round to 160000. She wonders if there is a simple formula to round any given number to only two significant digits.

Of course, it depends on what your definition of "simple" is. Fact of the matter, though, is that there are several different formulas you can use to get the desired result. Assuming that your original value is in cell A1, you can use any of the following representative formulas:

=ROUND(A1/(10^(INT(LOG10(ABS(A1)))+1)),2)*(10^(INT(LOG10(ABS(A1)))+1))
=ROUND(A1,-(INT(LOG(ABS(A1),10))+1)+2)
=FIXED(A1,1-INT(LOG10(ABS(A1))))
=ROUND(A1,1-INT(LOG(ABS(A1))))

These formulas will work with either positive or negative values just fine. The LOG (or LOG10) function is used to determine the number of digits either to the left or right of the decimal place before the first significant digit occurs. The INT of that function actually provides a number that is one less than the number of digits required, so that is why the value has 1 added to it. We can then round using that number of digits.

If you think that you may want to use a different number of significant digits than two, then you can use either of the following formulas:

=ROUND(A1,2-INT(LOG(ABS(A1)))+1)
=ROUND(A1,2-INT(LOG10(ABS(A1)))+1)
=FIXED(A1,2-INT(LOG10(ABS(A1)))-1)

All you need to do is change the 2 to reflect any number of significant digits you want. More information about significant digits in Excel can be found here:

<href="https://excel.tips.net/T001983_Thoughts_and_Ideas_on_Significant_Digits_in_Excel.html">http://excel.tips.net/T001983

ExcelTips is your source for cost-effective Microsoft Excel training. This tip (10396) applies to Microsoft Excel 97, 2000, and 2003. You can find a version of this tip for the ribbon interface of Excel (Excel 2007 and later) here: Rounding to Two Significant Digits.