Significant Figures Calculator (Sig Fig Counter and Rounder)
Count the significant figures in a number, round it to any number of sig figs, and see it in scientific notation.
Non-zero digits are always significant, zeros between them are significant, leading zeros never are, and trailing zeros count only when there is a decimal point. So 0.004560 has 4 significant figures (4, 5, 6 and the final 0), 1,020 has 3, and 1,020.0 has 5.
Free, runs in your browser. Nothing you enter is uploaded.
How to use it
- Enter the number.
- Choose how many sig figs to round to.
- Read the count and rounded value.
What you enter
- A number
- Target sig figs
What you get
- Count
- Rounded value
- Scientific notation
Formula
Rules: non-zero digits count; zeros between non-zero digits count; leading zeros do not; trailing zeros count only with a decimal point.
Significant figures express measurement precision; results should not carry more sig figs than the least precise measurement they derive from.
Worked example
Input: 0.004560 → 3 s.f.
Result: 4 significant figures · rounded 0.00456 · 4.560 × 10⁻³
Leading zeros are placeholders; the trailing zero after the decimal point is significant.
Questions
How many significant figures does 100 have?
Ambiguous — one by the strict rule. Write 1.00 × 10² or 100. (with a decimal point) to show three.
How many sig figs should I report?
As many as the least precise measurement in the calculation; for multiplication/division match the fewest sig figs, for addition/subtraction match the fewest decimal places.
How do you round to 3 significant figures?
Find the third significant digit and look at the digit after it: 5 or more rounds up, less than 5 leaves it. 0.0045678 to 3 s.f. is 0.00457, and 123,456 is 123,000 (1.23 × 10⁵).
Are zeros significant figures?
Zeros between non-zero digits are (101 has 3). Leading zeros are not (0.05 has 1). Trailing zeros are significant only after a decimal point (2.50 has 3, 250 has 2 unless written 250. or 2.50 × 10²).
Limitations
- Trailing zeros in integers without a decimal point (e.g. 1200) are treated as ambiguous and not counted; write 1.200 × 10³ to make them significant.
References
- IUPAC (2007). Quantities, Units and Symbols in Physical Chemistry, 3rd ed. RSC.
Related reading
- How to Report Statistical Results in Lab Report Text
- Lab Report Statistical Reporting: 10 Common Errors
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All free tools · By Dr. Zubair Khalid, DVM, MS, PhD.