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Significant Figures Calculator
Count significant figures in a written number, or round to between 1 and 14 sig figs. Handles trailing zeros, decimals, and scientific notation.
Try 0.00450, 100., or 1.20e3. A decimal point makes trailing zeros count.
Enter a number to count its significant figures.
Enter a number to count its significant figures.
This significant figures calculator is for science class, when a lab number has to be counted or rounded the way it was written. Nonzero digits count, zeros between them count, and leading zeros do not. Trailing zeros count only when the number has a decimal point, so 100 has 1 significant figure, 100. has 3, and 100.0 has 4. In scientific notation the coefficient carries the sig figs: 1.20 × 10³ and 1.20e3 each have 3. Rounding keeps a chosen count from 1 to 14 and writes ambiguous trailing zeros in scientific notation, so 1995 rounded to 2 significant figures is 2.0 × 10³.
How to count significant figures
Significant figures, also called sig figs or significant digits, are the digits in a written number that carry precision. Nonzero digits count. Zeros trapped between nonzero digits count. Leading zeros, which only hold a place before the first nonzero digit, do not count. 0.00450 has 3 significant figures: the digits that count are 4, 5, and the final 0.
Trailing zeros count only when the number has a decimal point. 100 has 1 significant figure, because those zeros have no decimal point. 100. has 3, because the decimal point at the end makes the zeros significant. 100.0 has 4. 1.20 has 3, since the zero after the decimal counts. A whole number such as 15 has 2 significant figures under the standard written-number rule. Both digits are nonzero. The trailing-zero rule is about zeros, and 15 has none.
Scientific notation keeps the count clear
In scientific notation the coefficient carries the significant figures, and the power of 10 does not add any. 1.20 × 10³ has 3 significant figures, the same digits as 1.20. Type it as 1.20e3, as 1.20 × 10^3, or with a superscript, 1.20 × 10³. A plain 2000 has 1 significant figure. Written as 2.0 × 10³ it has 2, and written as 2.00 × 10³ it has 3. Use that form when trailing zeros would otherwise be ambiguous.
Rounding to a chosen number of sig figs
To round to a chosen count, keep that many significant digits, then look at the next digit. Less than 5 means the last kept digit stays. 5 or more means it rounds up. 1.234 rounded to 3 significant figures is 1.23, because the next digit is 4. 0.001234 rounded to 2 significant figures is 0.0012, because the next digit is 3. The leading zeros still do not count.
1995 rounded to 2 significant figures becomes 2000, because the hundreds digit rounds up from 9 and the value carries to 2000. Written as 2000, the trailing zeros are ambiguous: the usual rule would count only 1 significant figure. The calculator writes 2.0 × 10³ so the result still has exactly 2 significant figures. An equals sign means the rounded value is the same number you typed. The sign ≈ means rounding changed it.
Frequently Asked Questions
How many significant figures does 0.00450 have?
0.00450 has 3 significant figures. The leading zeros do not count. The digits that count are 4, 5, and the trailing 0, and that last zero counts because the number has a decimal point.
How many significant figures are in 100?
100 has 1 significant figure. The zeros are trailing zeros with no decimal point, so they do not count. 100. has 3 significant figures, and 100.0 has 4, because a decimal point makes those zeros significant.
How many significant figures does 1.20e3 have?
1.20e3 has 3 significant figures. It is the same number as 1.20 × 10³. In scientific notation the coefficient 1.20 carries the count, and the power of 10 does not add a digit. The trailing zero in 1.20 counts because the coefficient has a decimal point.
How do you round 1995 to 2 significant figures?
1995 rounded to 2 significant figures is 2.0 × 10³. The first two significant digits are 1 and 9, and the next digit is 9, so 19 rounds up to 20. The value is 2000, but 2000 would be read as 1 significant figure, so scientific notation keeps the count at 2.
How many significant figures does 15 have?
15 has 2 significant figures. Under the standard written-number rule, a whole number is counted from the digits that are written. The trailing-zero rule is about zeros, and 15 has none, so both the 1 and the 5 count. Sig figs and significant digits are two names for the same digits.