Significant Figures

Rules

1) All non-zero digits (1, 2, 3, 4, 5, 6, 7, 8, 9) are significant.
2) Zeros between non-zero digits are significant.
3) Zeros before the first non-zero digit are not significant.
4) In a decimal, zeros after non-zero digits are significant.
5) In an integer, zeros after non-zero digits may or may not be significant.
Examples s.f Remarks
456 3
Rule 1
1.345 4
10204 5
Rule 2
1.406 4
0034 2
Rule 3
0.00546 3
1.30 3
Rule 4
1.400 4
1300 2,3,4 Rule 5
Reasons for being 2 or 3 s.f,
Round off 1296 to 2 s.f => 1300,
Round off 1296 to 3 s.f => 1300

Note that for rule (5), we can express an integer in standard form to avoid this ambiguity.

i.e 1300 = 1.3 * 103 (2s.f)
              = 1.30 * 103 (3s.f)
              = 1.300 * 103 (4s.f)

Also, note that in Physics, all the final answer should be in 2 or 3 s.f.
Excel@Physics