Scientific Significant Figures Calculator
Significant figures determine the precision of a measurement and ensure that calculated results are not reported with more precision than the measurements justify. This calculator rounds any number to a specified number of significant figures and displays the result in both standard decimal notation and scientific notation. It follows the rounding rules set out in the NIST/SEMATECH e-Handbook of Statistical Methods (Section 1.3.5.4).
Significant figure rounding rules (NIST)
To round a number to n significant figures:
- Find the n-th significant digit from the left.
- Look at the digit immediately after it. If it is 5 or greater, round up; otherwise truncate.
- Replace all following non-significant digits with zeros (for integers) or remove them (for decimals).
rounded = round(number, -(floor(log10(|number|)) - n + 1))
Significant figures rules summary
- Non-zero digits are always significant (e.g., 123 has 3 sig figs).
- Zeros sandwiched between non-zero digits are significant (e.g., 1,003 has 4 sig figs).
- Leading zeros before the first non-zero digit are not significant (e.g., 0.0042 has 2 sig figs).
- Trailing zeros after a decimal point are significant (e.g., 1.500 has 4 sig figs).
- Trailing zeros in a whole number may or may not be significant; use scientific notation to make this explicit.
Significant figures: frequently asked questions
What are significant figures?
Significant figures (sig figs) are the digits in a number that carry meaning contributing to its precision. All non-zero digits are significant. Zeros between non-zero digits are significant. Leading zeros are not significant. Trailing zeros in a decimal number are significant.
How do I count significant figures?
Rules: (1) All non-zero digits are significant. (2) Zeros between non-zero digits are significant (e.g., 1,002 has 4 sig figs). (3) Leading zeros are not significant (e.g., 0.0025 has 2 sig figs). (4) Trailing zeros after a decimal point are significant (e.g., 2.50 has 3 sig figs).
How many sig figs should I use in scientific calculations?
The result of multiplication or division should have the same number of significant figures as the measurement with the fewest sig figs. For addition and subtraction, the result should have the same number of decimal places as the measurement with the fewest decimal places.
What is scientific notation and when should I use it?
Scientific notation expresses a number as a coefficient between 1 and 10 multiplied by a power of 10 (e.g., 1.23 x 10^4). It is used for very large or very small numbers, and it makes the number of significant figures explicit.
What is the NIST recommendation for significant figures in measurement?
NIST recommends reporting measurement results with an uncertainty statement and rounding to no more decimal places than justified by the measurement uncertainty. The NIST/SEMATECH e-Handbook of Statistical Methods provides detailed guidance on uncertainty and significant figures.
Official sources
- NIST/SEMATECH e-Handbook of Statistical Methods, significant figures and rounding: NIST e-Handbook Section 2.3.5.4.
- NIST Special Publication 811, Guide for the Use of the International System of Units (SI): NIST SP 811.
Reviewed by the CalculatorHub team, edited by James Graham, 14 June 2026. See our methodology.