A number has as many significant figures as the count of digits that are meaningful in showing its precision, starting from the first non‑zero digit on the left to the last digit that is known (including certain zeros).

Core idea

  • Significant figures are all digits that carry information about a measurement’s precision.
  • To find how many significant figures a number has, you apply a small set of rules rather than a single formula.

Quick rules to count them

  • All non‑zero digits are significant (e.g., 211.8 has 4 significant figures).
  • Zeros between non‑zero digits are significant (e.g., 20 007 has 5 significant figures).
  • Leading zeros (zeros before the first non‑zero digit) are not significant (e.g., 0.0075 has 2 significant figures: 7 and 5).
  • Trailing zeros in a number with a decimal point are significant (e.g., 98.70 has 4 significant figures; 230.00 has 5).
  • Trailing zeros in a whole number without a decimal may or may not be significant unless extra notation (like a decimal point or scientific notation) is used; for clarity, 4.500 × 10³ clearly has 4 significant figures.

Why “how many” depends on the number

Because the rules depend on where zeros appear and whether there is a decimal point, the same digits can have different significant‑figure counts in different forms.

For example, 4500, 4.5 × 10³, and 4.500 × 10³ can represent 2, 2, and 4 significant figures respectively, depending on how precisely the value is meant.

If you share a specific number (like 0.00450 or 1200), I can tell you exactly how many significant figures it has and why.