Count sig figs instantly — and round any number to N significant figures
Enter a Number
Results
Digit breakdown
Red = significant | Strikethrough = not significant
Rounded to 3 significant figures
| Digit | Significant? | Reason |
|---|---|---|
| 0 | No | Leading zero |
| 0 | No | Leading zero |
| 2 | Yes | Non-zero digit |
| 0 | Yes | Captive zero |
| 4 | Yes | Non-zero digit |
| 5 | Yes | Non-zero digit |
| 6 | Yes | Non-zero digit |
| 0 | Yes | Trailing zero after decimal |
| 0 | Yes | Trailing zero after decimal |
Sig Fig Rules
A significant figures calculator helps students, scientists, and engineers count sig figs accurately and round numbers to the correct precision. Whether you are working on a chemistry lab report, a physics problem set, or an engineering calculation, this tool instantly identifies every significant digit in your number, explains why each digit counts or does not, and rounds the result to however many sig figs you need.
Leading zeros are never significant, so the two zeros before 4 do not count. The digits 4, 2, and the trailing zero after the decimal point all count — giving 0.00420 exactly 3 significant figures.
It depends on context. Without a decimal point, trailing zeros in whole numbers are ambiguous. This calculator conservatively treats them as not significant (so 1300 has 2 sig figs). Writing '1300.' with an explicit decimal point would make all four digits significant.
Identify the third significant digit (8), then look at the next digit (4). Since 4 < 5, round down, giving 6.78. The calculator handles this automatically — just type the number and set N to 3.
Captive zeros (also called trapped or sandwiched zeros) are zeros that sit between two non-zero digits, such as the zero in 4.06 or 1002. Because they represent a measured value between known non-zero digits, they must be counted as significant.