Round to 2 Significant Figures
Learn how to round any number to 2 significant figures with clear rules, worked examples, and common mistakes for decimals, whole numbers, and scientific notation.
Step-by-step explanation
Ignore leading zeros and find the first non-zero digit. That digit is the first significant figure.
Count one more significant digit to the right. Those first two significant digits are the digits you keep.
Look at the next digit after the second significant digit. If it is 5 or greater, increase the second significant digit by 1. If it is 4 or less, leave it unchanged.
Replace or drop the remaining digits while preserving place value. For large whole numbers, scientific notation is often the clearest way to show exactly 2 significant figures.
Worked examples
Ignore the leading zeros, keep 4 and 5, then look at 6. Because 6 is at least 5, 45 rounds up to 46.
Keep 7 and 9, then look at 8. The 9 rounds up through a carry, so scientific notation shows the result as exactly 2 significant figures.
The first two significant digits are 9 and 9. The next digit is 7, so the value rounds up to 1.0, where the trailing zero preserves 2 significant figures.
Keep 1 and 2, then look at 3. Since 3 is less than 5, the result stays at 12 tens. Scientific notation avoids ambiguity.
Keep 9 and 9, then look at 5. Rounding up creates 10; use 1.0 x 10^1 if you need to prove exactly 2 significant figures.
Why this answer is correct
Why the third significant digit matters
Rounding to 2 significant figures means the first two meaningful digits stay in the answer. The next significant digit decides whether the second kept digit stays the same or increases by one.
Why leading zeros do not change the process
Leading zeros only place the decimal point. In 0.004567, the first significant digit is 4, not 0. That is why the same four-step method works for tiny decimals, ordinary decimals, and large whole numbers.
When scientific notation is better
Whole-number answers such as 120, 8000, or 10 can be ambiguous. Scientific notation makes the precision explicit: 1.2 x 10^2, 8.0 x 10^3, and 1.0 x 10^1 each show exactly 2 significant figures.
Common mistakes to avoid
Rounding to 2 decimal places instead of 2 significant figures.
Counting leading zeros in numbers like 0.004567.
Dropping a needed trailing zero, such as writing 1 instead of 1.0 when the answer needs 2 significant figures.
Writing a large whole-number answer such as 8000 when the reader needs to know whether it has 1, 2, 3, or 4 significant figures.
Rounding intermediate calculation steps instead of rounding only the final result.
Frequently asked questions
What does round to 2 significant figures mean?
It means the final answer should keep exactly two meaningful digits. You keep the first two significant digits and use the next digit to decide whether to round the second one up.
Is rounding to 2 significant figures the same as 2 decimal places?
No. Significant figures count meaningful digits from the first non-zero digit. Decimal places count digits after the decimal point.
What is 0.004567 rounded to 2 significant figures?
0.004567 rounded to 2 significant figures is 0.0046.
What is 7982 rounded to 2 significant figures?
7982 rounded to 2 significant figures is 8.0 x 10^3. Writing 8000 alone can be ambiguous, so scientific notation is clearer.
How do I show exactly 2 significant figures in a whole number?
Use scientific notation when trailing zeros might be ambiguous. For example, write 120 as 1.2 x 10^2 and 8000 as 8.0 x 10^3.