Significant Figures Calculator

Rules for significant figures

1. All non-zero digits are significant.
2. Zeros between non-zero digits are significant (1,005 has 4).
3. Leading zeros are never significant (0.0045 has 2).
4. Trailing zeros after a decimal point are significant (2.50 has 3).
5. Trailing zeros in a whole number with no decimal point are ambiguous (1,200 may have 2, 3 or 4).

Worked example

0.004560 has 4 significant figures: the leading zeros do not count, but the final zero after the decimal does. Rounded to 2 sig figs it is 0.0046.

Sig figs in calculations

• Multiplying or dividing: round the answer to the fewest significant figures in any input.
• Adding or subtracting: round to the fewest decimal places in any input.

Frequently asked questions

How many sig figs are in 100?

It is ambiguous: at least 1. Writing 100. or 1.00 × 10² shows 3.

Are exact numbers limited by sig figs?

No. Counted values and defined constants, like 12 inches in a foot, have unlimited significant figures.

How do I round to 3 sig figs?

Keep the first three significant digits and round based on the next digit: 0.012345 becomes 0.0123.

Why use scientific notation?

It shows exactly which digits are significant: 1.20 × 10³ clearly has 3.