Significant Figures Calculator
Count the significant figures in a number, and round it to however many significant figures you need.
Rules for counting significant figures
All non-zero digits are always significant. Zeros between non-zero digits are always significant (like the zero in 105). Leading zeros (before the first non-zero digit) are never significant — they just indicate the decimal place. Trailing zeros are significant only if there's a decimal point present, which is why 100 is ambiguous (commonly treated as 1 sig fig) while 100.0 is unambiguous (4 sig figs).
This calculator follows the standard convention: trailing zeros without a decimal point are treated as not significant, since that's the most common teaching convention — though some contexts use bar notation or scientific notation to remove this ambiguity entirely.
Why significant figures matter in science
Significant figures communicate the precision of a measurement — reporting a result with more sig figs than your measuring instrument can support implies false precision, while reporting too few loses meaningful information. When performing calculations with measured values, results are generally rounded to match the precision of the least precise input.
This is especially important in chemistry, physics, and engineering, where reporting an answer with the wrong number of significant figures can be marked as technically incorrect even if the underlying math is right.
Frequently asked questions
Why is '100' ambiguous for significant figures?
Without a decimal point, it's unclear whether the trailing zeros are meant to be significant or are just placeholders — standard convention treats them as not significant (1 sig fig), though scientific notation (1 × 10²) removes the ambiguity entirely.
Are leading zeros ever significant?
No — leading zeros (before the first non-zero digit) are never significant. They only indicate the position of the decimal point, as in 0.0025, which has 2 significant figures.