MATH · SIGNIFICANT FIGURES

Significant Figures Calculator

Count significant figures in any number or round to N sig figs instantly. Handles leading zeros, trailing zeros, and scientific notation correctly.

Input number

Trailing zeros count — type "1.50" to get 3 sig figs.

01 Sig Figs
2
significant figures in 0.0025

About This Calculator

Significant figures (sig figs) represent the meaningful precision of a number. Use this calculator to instantly count the number of significant figures in any decimal or scientific-notation number, or to round a number to a specified number of sig figs.

How It Works

Choose COUNT mode to see how many significant figures a number has, or ROUND mode to reduce a number to N sig figs. Type the number exactly as written — trailing zeros matter. For scientific notation, type values like "1.23e4" and the mantissa digits are counted automatically.

The Formula

sig figs of x: count non-ambiguous significant digits per IUPAC convention Round to n: round(x, n−1−floor(log10(|x|))) decimal places

x
the input number
n
target number of significant figures

Frequently Asked Questions

Are trailing zeros significant?
It depends on where they appear. Trailing zeros AFTER a decimal point are always significant — 1.50 has 3 sig figs. Trailing zeros in a whole number WITHOUT a decimal point are ambiguous — 1200 is assumed to have 2 sig figs here, but could have 3 or 4. Use scientific notation (1.20 × 10³) or a decimal point (1200.) to make it unambiguous.
Are leading zeros significant?
No. Leading zeros (zeros before the first non-zero digit) are never significant. In 0.0025, only the 2 and 5 count, giving 2 significant figures.
Are zeros between non-zero digits significant?
Yes, always. In 1002, all four digits are significant because the zeros are 'sandwiched' between non-zero digits.
How do I round 3.14159 to 3 significant figures?
The first three significant figures are 3, 1, and 4. The next digit is 1 (< 5), so you round down: 3.14.
What is scientific notation?
Scientific notation writes numbers as a mantissa (1–10) times a power of 10 — e.g. 1.23 × 10⁴ = 12,300. The number of sig figs equals the number of digits in the mantissa. Type it as '1.23e4' in this calculator.