How rounding works
Rounding shortens a number to a chosen number of decimal places. Look at the first digit being dropped: if it is 5 or more, round the last kept digit up; otherwise leave it. Rounding 3.14159 to 2 places gives 3.14, because the next digit (1) is below 5.
Only that first dropped digit matters: rounding 2.4499 to one decimal place gives 2.4, not 2.5. Significant figures are easiest to see once a number is written with the scientific notation calculator.
How to use this calculator
Enter the number and how many decimal places to keep (0 rounds to a whole number). The result is the rounded value with the exact number of decimals requested. For division results you want to round, see the long division calculator.
Decimal places must be zero or more; negative entries are rejected. Negative numbers are accepted, and rounding acts on the magnitude in the usual way. Round only once, at the end of a calculation, so small errors do not accumulate.
Rounding rules and tie-breaking
This calculator uses standard round-half-up rules: a trailing 5 rounds the kept digit upward. Rounding to 0 places gives the nearest whole number, while more places keep more precision. Rounding always reports the requested number of decimals, even trailing zeros.
Other conventions exist. Banker's rounding sends an exact half to the nearest even digit, which prevents a systematic upward bias when many values are rounded and summed — accounting and some statistical software use it for that reason. Round-half-up is the rule taught in schools and used in most everyday work, which is why it is applied here. Repeating decimals are the usual reason rounding is needed at all, as the fraction to decimal calculator quickly shows.
Frequently asked questions
- What is 3.14159 rounded to 2 decimal places?
- 3.14. The third decimal digit is 1, which is below 5, so the second digit stays the same.
- How do I round to a whole number?
- Set decimal places to 0. The calculator returns the nearest integer.
- What rounding rule does this use?
- Round-half-up: when the dropped digit is 5 or more, the last kept digit is increased by 1.
- Why does the answer show trailing zeros?
- It shows exactly the number of decimal places you asked for, so 2.5 rounded to 2 places appears as 2.50.
- How is rounding different from truncating?
- Truncating simply cuts off the extra digits, while rounding looks at the first dropped digit and may increase the last kept one. Truncating 3.14159 to two places gives 3.14 as well, but truncating 3.999 gives 3.99 where rounding gives 4.00.