Counting significant figures
- All non-zero digits count: 347 has 3.
- Zeros between non-zero digits count: 4007 has 4.
- Leading zeros never count: 0.0045 has 2.
- Trailing zeros after a decimal point count: 0.00450 has 3, and 2.50 has 3.
- Trailing zeros in a whole number without a decimal point are ambiguous: 1200 could have 2, 3 or 4.
Scientific notation removes the doubt
Write 1200 as 1.2 × 103 for 2 significant figures, or 1.200 × 103 for 4. Every digit shown in the number before × 10 is significant.
Rounding results
- Multiplying and dividing: keep as many significant figures as the least precise value. 4.56 × 1.4 = 6.384, which rounds to 6.4.
- Adding and subtracting: keep as many decimal places as the value with the fewest. 12.11 + 0.3 = 12.41, which rounds to 12.4.
- Round only at the end of a calculation, not at each step.
- Exact numbers, such as counted items or defined conversions, do not limit the result.
Calculators
The Significant Figures Calculator counts and rounds any number. The Scientific Notation Converter and the Engineering Notation Converter write it in either form.