What are significant figures?

Significant figures are the digits in a number that carry meaningful information about its precision. They indicate how precisely a measurement was made.

How many sig figs does 100 have?

It is ambiguous. It could be 1, 2, or 3. Writing 1.00 × 10² (3 sig figs) or 1 × 10² (1 sig fig) removes the ambiguity.

Are trailing zeros significant?

Trailing zeros after the decimal point are significant (2.50 has 3 sig figs). Trailing zeros in a whole number without a decimal point are ambiguous.

How do I round to a certain number of sig figs?

Count from the first non-zero digit. At the desired position, round normally (5 or above rounds up). Replace remaining digits with zeros if before the decimal.

Why are sig figs important in science?

They communicate the precision of measurements. Reporting too many digits implies a precision that the instrument does not have, which misleads other scientists.

Do exact numbers have sig figs?

Exact numbers like counting (3 apples) or defined values (1 inch = 2.54 cm exactly) have infinite significant figures and do not limit the result's precision.

Significant Figures Calculator

Count significant figures and round numbers to a specified number of sig figs. Review how precision rules apply to each digit.

Enter a Numbere.g. 0.004560, 1500, 3.00e8

Round to (sig figs)

Arithmetic Operation

Significant Figures

In "0.004560"

Scientific Notation

4.560e-3

4 sig figs shown

Rounded to 3 Sig Figs

0.00456

From original value

Rounded (Scientific)

4.56e-3

3 sig figs in sci notation

Numeric Value

0.0045600000

Parsed numeric representation

Precision Level

High

4 sig figs indicates high-precision measurement

Digit-by-Digit Breakdown

0

.

0

0

4

5

6

0

Digit	Significant?	Rule
0	✗ No	leading zero — not significant
0	✗ No	leading zero — not significant
0	✗ No	leading zero — not significant
4	✓ Yes	non-zero digit — always significant
5	✓ Yes	non-zero digit — always significant
6	✓ Yes	non-zero digit — always significant
0	✓ Yes	trailing zero after decimal — significant

Operation	Rule for Sig Figs	Example
× or ÷	Use fewest sig figs from inputs	2.5 × 1.234 = 3.1 (2 sf)
+ or −	Use fewest decimal places from inputs	12.1 + 1.234 = 13.3 (1 dp)
log	Decimal places in result = sig figs of input	log(300) = 2.48 (1 sf → 1 dp)
Powers	Same sig figs as the base	2.5² = 6.3 (2 sf)

Planning notes, formulas, and examples

About the Significant Figures Calculator

The Significant Figures Calculator counts the number of significant figures (sig figs) in any number and rounds numbers to a desired number of significant figures. Significant figures represent the precision of a measurement.

Understanding significant figures is crucial in science, engineering, and any field where measurement accuracy matters. Reporting more digits than your instrument can measure implies false precision.

This calculator applies the standard sig fig rules: all non-zero digits are significant, zeros between non-zero digits are significant, leading zeros are never significant, and trailing zeros after the decimal point are significant.

When This Page Helps

Counting sig figs manually, especially with trailing zeros and scientific notation, is a common source of errors. This calculator applies the rules consistently and rounds accordingly.

How to Use the Inputs

Enter a number to count its significant figures.
View which digits are significant and why.
Optionally enter a target number of sig figs.
See the rounded result and its scientific notation.
Use the breakdown to understand each rule applied.

Formula used

Significant Figure Rules:
1. Non-zero digits are always significant
2. Zeros between non-zero digits are significant
3. Leading zeros are NOT significant
4. Trailing zeros after decimal point ARE significant
5. Trailing zeros in integers without decimal are ambiguous

Example Calculation

Result: 4 significant figures

In 0.004560, the leading zeros (0.00) are not significant. The digits 4, 5, 6 are significant. The trailing zero after 6 is significant because it follows the decimal point. Total: 4 sig figs.

Tips & Best Practices

Leading zeros never count as significant figures.
A trailing zero after the decimal IS significant (3.0 has 2 sig figs).
Use scientific notation to remove ambiguity (1.20 × 10³ = 3 sig figs).
In multiplication/division, use the fewest sig figs from the inputs.
In addition/subtraction, use the fewest decimal places from the inputs.
Exact numbers (counting, defined constants) have infinite sig figs.

Significant Figures in Calculations

When multiplying or dividing, the result should have the same number of sig figs as the input with the fewest. When adding or subtracting, the result should have the same number of decimal places as the input with the fewest.

Common Mistakes

The most frequent errors involve trailing zeros and leading zeros. Students often count leading zeros as significant or forget that 2.0 has more precision than 2.

Scientific Notation and Sig Figs

Scientific notation eliminates ambiguity. Writing 1.50 × 10³ clearly shows 3 sig figs, whereas 1500 is ambiguous.

Lab reports, calibration sheets, and engineering notes all depend on this distinction because the number of reported digits should match the precision the measurement method can support.

Sources & Methodology

Last updated: February 8, 2026

Frequently Asked Questions

Significant figures are the digits in a number that carry meaningful information about its precision. They indicate how precisely a measurement was made.