Significant figures calculator.

The counting rules

1. All non-zero digits are significant (237 has 3). 2. Zeros between non-zero digits are always significant (39,004 has 5). 3. Leading zeros, the ones in front of all the non-zero digits, are never significant (0.000416 has 3). 4. Trailing zeros are significant when the number has a decimal point (620.0 has 4, 19.000 has 5). 5. A whole number with trailing zeros and no decimal point is ambiguous: 1400 may have 2, 3 or 4. Scientific notation settles it, since 1.4 × 10³ has two and 1.400 × 10³ has four. This calculator reports the lowest count for such a number (2 for 1400) and shows the range.

Counted or defined numbers are exact and have unlimited significant figures: 4 counted objects is 4.000…, and the 12 in 12 inches per foot is exact. They never limit an answer, which is why the sig fig arithmetic calculator has an exact-number box.

Rounding to significant figures

Keep the first n significant digits and look at the digit after them. If it is 6 to 9, or 5 followed by anything other than zeros, round the last kept digit up. A bare 5 is a tie: the usual classroom rule rounds it up (2.5 to 1 sig fig is 3), and half-to-even, which gives 2, is the alternative that avoids a built-in upward bias. Follow your instructor. Rounding is done on the digits you typed, not on a floating-point number, so 2.675 to 3 sig figs is 2.68 as you would write it by hand.

Rounding a whole number such as 123,456 to 3 sig figs gives 123,000, but the trailing zeros there are placeholders. The result is therefore also shown in scientific notation (1.23 × 10⁵), which is unambiguous.

Worked examples

Counting: 237 has 3, 0.008 has 1, 39,004 has 5, 620.0 has 4, 1400 has 2 (up to 4) and 1.400e3 has 4. Rounding to 3 sig figs: 123,456 becomes 123,000 (1.23 × 10⁵), 0.0123456 becomes 0.0123 and 99.96 becomes 100, written 1.00 × 10² to show that all three digits are significant. Rounding 3.14159 to 2 decimal places gives 3.14, and 1234 to −2 decimal places (the hundreds) gives 1200.

Sources, opened 8 October 2026: Chemistry LibreTexts, 2.3: Significant Figures - Writing Numbers to Reflect Precision (the significant figure rules, trailing-zero ambiguity of 1400 and exact numbers); Wikipedia, Rounding (round half up as a widely used tie-breaking rule, round half to even as the rule without bias toward or away from zero).

Note: Educational calculator. Textbooks differ on the significant figures in zero itself (counted here as 1) and on tie-breaking, so follow your instructor’s convention.