Significant Figures Calculator
Count the significant figures in any number and round to a specific number of sig figs.
Essential for science and engineering.
Significant figures (sig figs) are the meaningful digits in a measured or calculated number. They indicate the precision of a measurement — not its magnitude. Proper sig fig usage is fundamental in science, engineering, and laboratory work, where reporting false precision is as misleading as reporting inaccurate results.
Rules for counting significant figures:
- All non-zero digits are significant (e.g., 452 has 3 sig figs)
- Zeros between non-zero digits are significant (e.g., 4,005 has 4 sig figs)
- Leading zeros are never significant (e.g., 0.0045 has 2 sig figs)
- Trailing zeros after a decimal point are significant (e.g., 3.500 has 4 sig figs)
- Trailing zeros in a whole number are ambiguous without a decimal (e.g., 2400 may have 2, 3, or 4 sig figs)
Rounding to N significant figures:
Identify the Nth significant digit → round based on the digit that follows
If the following digit is ≥ 5, round up. If < 5, round down.
Worked examples:
- Round 34,567 to 3 sig figs: 3rd digit is 5, next digit is 6 → 34,600
- Round 0.0047382 to 3 sig figs: 3rd significant digit is 3, next digit is 8 → 0.00474
- Round 1.00495 to 4 sig figs: 4th digit is 9, next digit is 5 → 1.005
Rules for arithmetic with sig figs:
- Multiplication/Division: Result keeps the fewest sig figs of any input
- 4.56 × 1.4 = 6.384 → reported as 6.4 (2 sig figs)
- Addition/Subtraction: Result keeps the fewest decimal places of any input
- 12.52 + 0.4 = 12.92 → reported as 12.9 (1 decimal place)
Scientific notation and sig figs: Scientific notation removes all ambiguity. 2400 written as 2.4 × 10³ has exactly 2 sig figs; written as 2.400 × 10³ it has 4 sig figs.
Where sig figs matter most: chemistry lab reports, physics measurements, engineering tolerances, and any published scientific data where reproducibility must be communicated.