Significant Figures Reference Sheet
For measured numbers, significant figures relate the certainty of the measurement. As the number of
significant figures increases, the more certain the measurement.
Rules for Counting
1. ALL non-zero numbers (1,2,3,4,5,6,7,8,9) are ALWAYS significant.
Example: 15 = 2 sig figs
145 = 3 sig figs
2. Zeros between nonzero digits are ALWAYS significant. (Squished zeros count!)
Example: 105 = 3 sig figs
5005 = 4 sig figs
3. ALL zeros to the left of the first non zero (1,2,3,4,5,6,7,8,9) are not significant.
Example: 0.0005 = 1 sig fig
0.0505 = 3 sig figs
4. If there is a decimal, zeros to the right of the last non zero are ALWAYS significant.
Example: 2.0 = 2 sig figs
0.500 = 3 sig figs
General Examples:
Number
# of Sig Figs
Rule(s)
48,923
5
1
3.923
4
1
900.06
5
1,2
0.0004
1
1,3
8.1000
5
1,4
501.040
6
1,2,4
3,000,000
1
1
10.0
3
1,4
0.004050
4
1,2,3,4
ADDING AND SUBTRACTING: Count the number of decimal places. Round to the lowest number of decimal
places. Remember, if trying to remove a figure from an answer, round up if 5 or higher.
Examples:
2.5 + 1 = 3.5 which rounds to 4
5.31 – 2.2 = 3.11 which rounds to 3.1
MULTIPLYING AND DIVIDING: Count the number of significant figures. Round to the lowest number of
significant figures. Remember, if trying to remove a figure from an answer, round up if 5 or higher.
Examples:
2.55 x 2 = 5.1 which rounds to 5
10.0 / 3.0 = 3.3333333 which rounds to 3.3
16.5 / 3 = 5.5 which rounds to 6
