Are trailing zeros significant?

It depends on the context. Trailing zeros after a decimal point are always significant (2.500 has 4 sig figs). Trailing zeros in whole numbers without a decimal point are ambiguous (1500 could be 2, 3, or 4 sig figs). Adding a decimal point makes them significant (1500. has 4 sig figs).

How do sig figs work in multiplication vs addition?

For multiplication and division, round the result to the same number of sig figs as the least precise factor. For addition and subtraction, round to the same number of decimal places as the least precise term. These different rules reflect how precision propagates in each operation.

What are exact numbers in sig fig calculations?

Exact numbers have infinite significant figures and never limit the precision of a calculation. Examples include counted quantities (12 eggs), defined conversions (100 cm in 1 m), and mathematical constants when defined exactly. Only measured values limit sig figs.

Why do we use significant figures?

Significant figures communicate the precision of a measurement. Reporting too many digits implies false precision. If your ruler measures to the nearest millimeter, reporting 5.0000 cm suggests precision you dont actually have. Sig figs keep results honest about measurement uncertainty.

How many sig figs does 100 have?

Without more context, 100 is ambiguous - it could have 1, 2, or 3 significant figures. To clarify: write 100. (3 sig figs), 1.0 × 10² (2 sig figs), or 1 × 10² (1 sig fig). In scientific work, always use notation that makes precision clear.

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Sig Fig Calculator

Count & calculate with significant figures

Last updated: February 27, 2026

Mode

Enter a number

Significant Figures

Digit Analysis

0.00450

SignificantNot significant

Rules Applied

✓Leading zeros are not significant
✓Non-zero digits are always significant
✓Trailing zeros after decimal point are significant

Digit-by-Digit Breakdown

0NOTLeading zeros are not significant

4SIGNon-zero digits are always significant

5SIGNon-zero digits are always significant

0SIGTrailing zeros after decimal point are significant

The 6 Rules of Significant Figures

Rule 1

All non-zero digits are significant

Example: 123 has 3 sig figs

Rule 2

Zeros between non-zero digits are significant

Example: 1002 has 4 sig figs

Rule 3

Leading zeros are never significant

Example: 0.0025 has 2 sig figs

Rule 4

Trailing zeros after decimal are significant

Example: 2.500 has 4 sig figs

Rule 5

Trailing zeros in whole numbers are ambiguous

Example: 1500 could be 2, 3, or 4 sig figs

Rule 6

Exact numbers have infinite sig figs

Example: 12 eggs, 100 cm in 1 m

Quick Reference Examples

How to Use the Sig Fig Calculator

The significant figures calculator helps you count sig figs in any number, round numbers to a specific number of significant figures, and perform arithmetic operations with correct sig fig rounding. Essential for chemistry, physics, and any scientific calculation where precision matters.

Understanding Significant Figures

Significant figures (sig figs) represent the precision of a measurement. They include all certain digits plus one uncertain digit. When you measure something, the number of sig figs tells others how precise your measurement actually was.

The 6 Rules of Significant Figures

Rule 1: All non-zero digits are significant. Example: 123 has 3 sig figs.
Rule 2: Zeros between non-zero digits are significant. Example: 1002 has 4 sig figs.
Rule 3: Leading zeros are never significant. Example: 0.0025 has 2 sig figs.
Rule 4: Trailing zeros after the decimal point are significant. Example: 2.500 has 4 sig figs.
Rule 5: Trailing zeros in whole numbers without a decimal are ambiguous. Example: 1500 could be 2, 3, or 4 sig figs.
Rule 6: Exact numbers (counting numbers, defined values) have infinite sig figs.

Sig Figs in Calculations

Different operations follow different rules for determining sig figs in the result:

Multiplication/Division: Round to the fewest sig figs of any number in the calculation.
Addition/Subtraction: Round to the fewest decimal places of any number in the calculation.

Common Examples

Here are some frequently confused examples:

0.00450 — 3 sig figs (the leading zeros are not significant, but the trailing zero after 5 is)
100 — Ambiguous (could be 1, 2, or 3 sig figs)
100. — 3 sig figs (the decimal point makes all zeros significant)
100.0 — 4 sig figs

Why Sig Figs Matter

Using proper significant figures prevents you from implying more precision than your measurements actually have. In scientific work, reporting 5.0000 when your instrument only reads to 5.0 misrepresents your data's accuracy.

Related Calculators

For converting between standard and scientific notation, use our scientific notation calculator. Need to perform calculations? Try our scientific calculator or percentage calculator.

Frequently Asked Questions

0.0050 has 2 significant figures. The leading zeros (before the 5) are not significant because they only serve as placeholders. The trailing zero after the 5 is significant because it comes after the decimal point and after a non-zero digit, indicating precision.