Significant Figures Calculator
Count the significant figures of a number, see which digits count, and round it to a chosen number of significant figures or decimal places — exactly.
The sig-fig count with each digit marked, the ambiguous-trailing-zero case explained, the number rounded to your sig figs and decimal places, scientific notation and a 1–6 sf ladder.
Example: 0.004560 has 4 significant figures (the leading zeros place the decimal, the last zero is measured) and rounds to 0.0046; 1200 has 2, 3 or 4 — written 1.200 × 10³ it has 4.
Which digits
were actually measured.
The counting rules, the one ambiguous case, and the two rounding conventions.
Counting
Non-zero digits are significant. Zeros between them are significant. Leading zeros are not — they only place the decimal point (0.004560 has four significant figures: 4, 5, 6, 0). Trailing zeros after a decimal point are significant, because writing them claims that precision.
The ambiguous case
Trailing zeros in a whole number without a decimal point — 1200 — may or may not be significant; the number alone cannot say. The page counts them as not significant and flags them. Scientific notation removes the doubt (1.2 × 10³ has two, 1.200 × 10³ has four), as does a trailing decimal point in some conventions.
Rounding
Rounding is done on the decimal digits as written, never on a binary float, so 0.996 to two figures is exactly 1.0. On an exact half, classrooms usually round away from zero (1.25 → 1.3); IEEE 754 and many standards round to the even digit (1.25 → 1.2). Both are offered and the page says which applied. Rounding to more figures than were written adds zeros the measurement never claimed, and says so. Nothing leaves the browser; the same four anonymous usage counts as the rest of the site apply.
SOURCES
- Conventional sig-fig rules taught in introductory chemistry and physics; rounding half away from zero (classroom) or half to even (IEEE 754 / ASTM E29 style), both offered
Last reviewed 20 September 2026. How results are checked: How we verify.