How this rounding calculator works
Rounding replaces a number with a nearby value that is simpler to read or store, keeping only as much detail as you need. You first choose what to round to — a fixed number of decimal places, a nearest unit such as ten or one hundred, or a custom multiple like 5 or 0.25 — and then a rounding mode that decides what happens when the value sits exactly halfway between two options.
The everyday rule is round half up: look at the first digit you are about to drop, and if it is 5 or more you round the kept part up, otherwise you leave it. Banker's rounding (round half to even) instead sends exact halves to the nearest even digit, which keeps large batches of numbers from drifting upward. Ceiling and floor always go up or down regardless of the digit, while truncate simply chops off the extra digits toward zero.
Reference note: this tool parses input as a JavaScript number, so values carry roughly 15–17 significant digits of precision. Some decimals (such as 2.675) cannot be stored exactly in binary, which can occasionally tip a borderline halfway case; for exact arbitrary-precision rounding use a dedicated decimal library.
Frequently asked questions
- How do I round a number?
- Decide what you are rounding to — a number of decimal places or a nearest unit such as 10 or 0.25 — then look at the first digit being dropped. With round half up, if that digit is 5 or more you round up, otherwise you round down. For example 3.14159 rounded to 2 decimal places is 3.14 because the next digit is 1.
- What is rounding half up?
- Round half up is the rule most people learn in school: when the part being dropped is exactly one half, you round away from zero to the larger magnitude. So 2.5 becomes 3 and 0.45 to one decimal place becomes 0.5. It is the default mode in this calculator.
- What is banker's rounding?
- Banker's rounding, also called round half to even, rounds a value that is exactly halfway to the nearest even digit instead of always rounding up. So 2.5 becomes 2 and 3.5 becomes 4. Spreading halves between up and down reduces cumulative bias, which is why it is used in finance and statistics.
- How do I round to the nearest 10?
- Divide the number by 10, round that result to a whole number, then multiply back by 10. For example 47 divided by 10 is 4.7, which rounds to 5, and 5 times 10 is 50. In this tool you can pick nearest ten directly, or enter 10 as a custom nearest multiple.
- What is the difference between round, floor and ceiling?
- Rounding moves a number to the closest target value, up or down depending on the dropped part. Floor always rounds down toward negative infinity, so 2.9 becomes 2. Ceiling always rounds up toward positive infinity, so 2.1 becomes 3. Truncate simply discards the extra digits toward zero, so -2.9 becomes -2.
- How do I round to 2 decimal places?
- Keep the first two digits after the decimal point and look at the third digit to decide the last kept digit. With round half up, 3.14159 becomes 3.14 because the third digit is 1, while 2.675 becomes 2.68. Set decimal places to 2 in this calculator to do it automatically.