1. Nonzero digits are always significant
Ex: 457 cm – 3 sig dits
2.5 g – 2 sig dits
2. Zeros between nonzero digits are always significant
Ex: 1005 kg – 4 sig dits
1.03 cm – 3 sig dits
3. Zeros at the beginning of a number are never significant – they only indicate the position of the decimal point.
Ex: 0.02 g – 1 sig dit
0.0026 L – 2 sig dits
4. Zeros that fall both at the end of a number and after the decimal point are always significant.
Ex: 0.0200 – 3 sig dits
3.0 mL – 2 sig dits
5. When a number ends in zeros but contains no decimal point, the zeros may or may not be significant.
Ex: 130 cm – 2or 3 sig dits
10,300 g – 3 or 5 sig dits
6. Exponential Notation resolves the ambiguity in #5 above.
Ex: 1.03 x 10 4 g – 3 sig dits
1.030 x 10 4 g – 4 sig dits
1.0300 x 10 4 g – 5 sig dits
7. Multiplication and Division
The answer must have the same number of sig dits as the measurement with the fewest sig dits
Ex: (6.221 cm)( 5.2
cm) = 32.3492 cm 2
Round off to 32 cm 2
8. Round Off
In rounding off numbers, look at the leftmost digit to be dropped:
1. If the leftmost digit to be removed is less than 5, the preceding number is left
2. unchanged.
Ex: Rounding 7.248 to 2 sig dits
Becomes 7.2
If the leftmost digit to be removed is 5 or greater, the preceding number is increased by 1.
Ex: Rounding 4.735 to 3 sig dits
Becomes 4.74

9. Addition and Subtraction
The answer cannot have more digits to the right of the decimal than any of the original numbers.
Ex: 20.
4
1.32
+ 8
10
3
2
4.722 Round off to 105