# Significant figures

How to calculate significant figures of a number? I got confuse as the number 28600 has 3 significant figure instead of 5. Anyone can explain?

• The number 28600 does not have any number of significant figures. It is an exact number. When you write a check for 28600 dollars, the bank will pay EXACTLY 28600 dollars or all hell breaks lose. When I order 28600 components from my electronics supplier, they will send me exactly 28600 components or I have a right to reject the shipment at their cost, which is why they have counting machines for this purpose. If you want to specify an accuracy for a number it's much better to do it explicitly like 28600+-1000. Jun 17, 2015 at 18:34
• More on significant figures. Apr 17, 2016 at 14:14

The number of significant digits in 28600 depends on what the error in the measurement is. If sigma = 15 Then we can write 28600(15) and there are 5 significant digits. If sigma = 1800 then we can write 28600 +-1800 and there are 3 significant digits. If sigma = 25000 then we can write 2.9(25)x10^4 and there are 2 significant digits. Significant digits are the work of the devil and cause much confusion. Calculate the uncertainty first and then you can calculate how many significant digits there are.

Jack

• OP doesn't mention anything about error here. Jul 22, 2015 at 13:24
• This is incorrect. 28600 has 3 significant digits regardless what the uncertainty is (unless it is an absolute number). If the uncertainty is (15), then writing it as 28600 is inappropriate because that has 3 sig digs. It should then be written as $2.8600\times10^4$, which has 5 sig digs.
– Jim
Jul 22, 2015 at 15:26
• @KyleKanos The question is tagged error-analysis. Mar 14, 2021 at 12:45
• If the error is large enough to affect the fourth digit, then the value only has four significant figures? Mar 14, 2021 at 12:50
• Is it correct to write “2.9(25)x10^4” if sigma = 25x10^**3**? Mar 14, 2021 at 12:52

It have 5 significant figures, as the zeros are present on right hand side of a numbers .

• Trailing zeros are generally regarded as insignificant, so it should be 3, not 5. Jun 17, 2015 at 13:54
• @kyle According to text book I read should 5.
– Nik
Jun 17, 2015 at 13:55
• Either your textbook is wrong or you misread it; trailing zeros are not significant. Jun 17, 2015 at 13:57
• Well, in the usual convention trailing zeros before the radix are not significant, but those after the radix are. Jun 17, 2015 at 21:45
• I consider the number 28600 to be ambiguous with regard to significant figures. That is why it is best to use scientific notation for such numbers, such as 2.86 x 10^4, which clearly has 3 significant figures. Feb 28, 2016 at 3:23