Round to 3 Significant Figures
Learn how to round any number to 3 significant figures with clear steps, worked examples, and common mistakes for decimals, whole numbers, and scientific notation.
Step-by-step explanation
Find the first non-zero digit. That digit is the first significant figure; any zeros before it are only placeholders.
Count three significant digits from that starting point. These are the digits that should remain in the rounded answer.
Look at the fourth significant digit. If it is 5 or greater, increase the third significant digit by 1. If it is 4 or less, leave the third digit unchanged.
Drop the remaining digits after rounding. For whole-number results with trailing zeros, use scientific notation when you need to show exactly 3 significant figures.
Worked examples
The first three significant digits are 2, 4, and 7. The fourth significant digit is 5, so 24.7 rounds up to 24.8.
Ignore the leading zeros, keep 4, 5, and 6, then look at 7. Because 7 is at least 5, the 6 rounds up to 7.
Keep 4, 3, and 2, then look at 5. Rounding up gives 433,000; scientific notation makes the 3 significant figures explicit.
Keeping 9, 9, and 9 then rounding on 5 creates a carry. The trailing zero in 10.0 or 1.00 x 10^1 preserves exactly 3 significant figures.
The first three significant digits are 9, 9, and 9. The fourth significant digit is 4, so the kept digits do not round up.
Why this answer is correct
Why the fourth significant digit controls the rounding
Rounding to 3 significant figures means the answer should keep three meaningful digits. The digit immediately after those three tells you whether the third kept digit should stay the same or increase by one.
Why 3 significant figures is not 3 decimal places
Three significant figures count meaningful digits from the first non-zero digit. Three decimal places count places after the decimal point. For example, 0.004567 to 3 significant figures is 0.00457, not 0.005.
Why scientific notation helps with large answers
Answers such as 433,000 or 10.0 can be misread if the trailing zeros are not clearly significant. Scientific notation shows the precision directly: 4.33 x 10^5 and 1.00 x 10^1 both contain exactly 3 significant figures.
Common mistakes to avoid
Rounding to 3 decimal places instead of 3 significant figures.
Counting leading zeros as significant in small decimals such as 0.004567.
Dropping a needed trailing zero after a carry, such as writing 10 instead of 10.0 when the result needs 3 significant figures.
Leaving large whole-number answers ambiguous when scientific notation would show the exact precision.
Rounding twice during a longer calculation. Keep extra digits while calculating, then round the final answer to 3 significant figures.
Frequently asked questions
What does round to 3 significant figures mean?
It means the final answer should keep exactly three meaningful digits. You keep the first three significant digits and use the fourth significant digit to decide whether to round the third one up.
What is 24.753 rounded to 3 significant figures?
24.753 rounded to 3 significant figures is 24.8 because the fourth significant digit is 5.
What is 0.004567 rounded to 3 significant figures?
0.004567 rounded to 3 significant figures is 0.00457. The leading zeros do not count as significant figures.
Is 3 significant figures the same as 3 decimal places?
No. Three significant figures count meaningful digits from the first non-zero digit, while three decimal places count fixed positions after the decimal point.
How do I show exactly 3 significant figures in a large whole number?
Use scientific notation when trailing zeros could be ambiguous. For example, write 433,000 as 4.33 x 10^5 to show exactly 3 significant figures.