Many students struggle with one common question in science and math: how to know how many significant figures a number has. At first glance, numbers may look simple, but zeros, decimals, and scientific notation can make counting significant figures confusing.
In this guide, you’ll learn an easy, step-by-step method to identify significant figures in any number, with clear rules and practical examples.
What Are Significant Figures?
Significant figures (also called sig figs) are the digits in a number that show how precise a measurement is.
They include:
- All certain digits
- The first uncertain digit
In simple terms, significant figures tell us how accurately a value was measured, not just its size.
Step 1: Identify Non-Zero Digits
The easiest rule to remember is:
👉 All non-zero digits are always significant.
Examples:
- 245 → 3 significant figures
- 6.38 → 3 significant figures
- 91.07 → 4 significant figures
This rule applies no matter where the digit appears.
Step 2: Check for Leading Zeros (Not Significant)
Leading zeros are zeros that appear before the first non-zero digit.
These zeros only show the position of the decimal point.
Examples:
- 0.0042 → 2 significant figures
- 0.00091 → 2 significant figures
👉 Leading zeros are not counted.
Step 3: Count Zeros Between Non-Zero Digits (Significant)
Zeros that appear between two non-zero digits are always significant.
Examples:
- 101 → 3 significant figures
- 2.05 → 3 significant figures
- 1002 → 4 significant figures
These zeros are sometimes called captive zeros.
Step 4: Look at Trailing Zeros
Trailing zeros appear at the end of a number, and their significance depends on whether a decimal point is present.
Without a decimal point:
- 1500 → 2 significant figures
- 700 → 1 significant figure
With a decimal point:
- 150.0 → 4 significant figures
- 7.00 → 3 significant figures
👉 Trailing zeros are significant only when a decimal point is shown.
Step 5: Use Scientific Notation for Clarity
Scientific notation removes all confusion about significant figures.
Examples:
- 4.50 × 10² → 3 significant figures
- 1.200 × 10³ → 4 significant figures
👉 Only the digits in the coefficient are counted.
Quick Checklist to Know How Many Significant Figures a Number Has
Use this simple checklist every time:
- Count all non-zero digits
- Ignore leading zeros
- Count zeros between non-zero digits
- Count trailing zeros only if a decimal point is present
- In scientific notation, count digits in the coefficient only
Common Mistakes Students Make
- Counting leading zeros as significant
- Ignoring trailing zeros after the decimal
- Assuming all zeros are insignificant
- Forgetting to use scientific notation
Avoiding these mistakes can greatly improve exam and lab accuracy.
Why Knowing Significant Figures Matters
Correct significant figures are essential in:
- Chemistry and physics calculations
- Lab reports and experiments
- Engineering and medical measurements
- Scientific research
Even if your math is correct, the wrong number of significant figures can make an answer incorrect.
Use an Online Significant Figures Calculator
Manually counting significant figures can be time-consuming and error-prone, especially with long decimals.
That’s why many students and professionals use an online significant figures calculator to double-check their answers.
These tools help:
- Count significant figures instantly
- Handle zeros correctly
- Reduce human errors
Final Thoughts
Knowing how many significant figures a number has becomes easy once you understand where the zeros are and what they mean.
With a little practice and the right rules, you can identify significant figures quickly and confidently.
For accuracy and speed, always verify your results when needed.
FAQs
How to tell how many significant figures are in a number?
To tell how many significant figures a number has, count all non-zero digits, include any zeros between non-zero digits, and count trailing zeros only if a decimal point is present. Do not count leading zeros. In scientific notation, only the digits in the coefficient are significant.
How many significant figures are there in 0.310 × 10³?
The number 0.310 × 10³ has 3 significant figures.
Only the digits in the coefficient (0.310) are counted. The digits 3, 1, and the trailing zero after the decimal point are all significant.
How many sig figs does 0.004500 have?
The number 0.004500 has 4 significant figures.
The leading zeros are not significant, but the digits 4 and 5, along with the two trailing zeros after the decimal point, are significant because they show precision.
How many significant figures does 699.06133000 have?
The number 699.06133000 has 11 significant figures.
All non-zero digits are significant, the zero between non-zero digits is significant, and the trailing zeros after the decimal point are also significant because a decimal point is present.