All measurements have an amount of certainty and uncertainty.
Rules
Determining significant figures (sig figs) can be daunting for some students.
Non zero numbers
All nonzero numbers are significant figures, no matter if they are before or after a decimal point.
For example,
2345 has 4 significant figures.
987 has 3 significant figures.
75.4 has 3 significant figures.
Zeros as Significant Digits
Leading zeros are never significant.
For example, 00004 has 1 significant figure.
Trailing zeros are significant when there is a decimal,
For example, 1000.0 has 5 significant figures.
Trailing zeros without a decimal, however, can be either significant or not significant.
To clarify, one may place a bar over the last significant zero.
For example, to clarify that 1000 has 4 significant figures, one would place a bar over the 0 farthest to the right.
Another way to clarify if trailing zeros are significant is to use Scientific_notation.
When one writes 1.00 x 103 it is made clear that the two trailing zeros are significant. If one were to write 1 x 103 it would be made clear that the trailing zeros are not significant.
Calculations
See significant figures calculations