Sig Fig Calculator
Type any number — including scientific notation like 5.20e-3 — and see how many significant figures it has, with every digit color-coded and each rule explained. Then round any number to 1–10 sig figs in plain and scientific notation.
Count significant figures
Significant figures
3sig figs
significantnot significant
- • 2 nonzero digits are significant — nonzero digits always count.
- • 3 leading zeros (before the first nonzero digit) are not significant — they only mark the decimal place.
- • 1 trailing zero is significant because the number has a decimal point.
Round to significant figures
Rounded to 3 sig figs
3.14
Scientific notation
3.14 × 100
The 5 rules of significant figures
| Rule | Example | Sig figs |
|---|---|---|
| 1. Nonzero digits are always significant | 234.5 | 4 |
| 2. Zeros between nonzero digits (captive zeros) are significant | 4,005 | 4 |
| 3. Leading zeros are never significant | 0.00520 | 3 |
| 4. Trailing zeros are significant only when the number has a decimal point | 25.00 | 4 |
| 5. Trailing zeros without a decimal point are ambiguous — assumed not significant | 4,500 | 2 |
Worked example: 0.00520
Take 0.00520. The three zeros at the front are leading zeros — they appear before the first nonzero digit and only position the decimal point, so they do not count. The 5 and 2 are nonzero digits and always count. The final 0 is a trailing zero in a number that has a decimal point, so it counts too. Result: 3 significant figures — which is exactly why a scientist writes 0.00520 instead of 0.0052: the extra zero deliberately claims one more digit of measured precision. In scientific notation the same number is 5.20 × 10⁻³, where all three digits of the mantissa are visibly significant.
Rounding works from the left: to round 0.0052047 to 3 sig figs, keep the first three significant digits (5, 2, 0), look at the next digit (4, less than 5) and round down: 0.00520.
More math tools
Sig figs go hand in hand with scientific notation — the exponent calculator handles the powers of ten and the logarithm calculator goes the other way. For rounding to a fixed decimal place instead of significant figures, use the rounding calculator, and for developer time math the Unix timestamp converter and subnet calculator have you covered.