Rounding is not laziness — it reflects how precisely you actually know a number. Reporting more decimal places than your data supports creates false accuracy.
Basic rounding rules
Look at the digit after the place you are rounding to:
- 5 or higher → round up
- 4 or lower → round down
Example
Round 3.847 to one decimal place → 3.8 (the next digit is 4). Round 3.857 to one decimal place → 3.9 (the next digit is 5).
Significant figures
Count meaningful digits from the first non-zero digit.
- 0.00450 has three significant figures (4, 5, and the trailing 0)
- 1200 might have two or four, depending on context — use scientific notation when precision matters
Practical rule
Your final answer should not have more precision than your least precise input.