Rounding calculator
Type in a number and choose how to round it. You will see the rounded number, the change with a plus or minus sign, and both positions on a number line.
Updated ·Sources verified
Round one number to 0–4 decimal places or to the nearest 1, 10, 100 or 1,000. Choose Nearest, Round up or Round down, then see whether the rounded value is higher or lower.
Rounded value
3.14
Difference: -0.00159
The rounded value updates as you type. The number line shows where your number started and where it ended. Difference is the rounded value minus your original number: + means higher and − means lower.
How does it work?
Nearest sends an exact halfway value to the higher result: 2.5 → 3 and −2.5 → −2. Round up chooses the higher result on the number line; Round down chooses the lower one. If the number already fits the chosen rounding, it does not change.
The rounding rule
- x
- The number you enter.
- u
- The size of each rounding step: a whole for 0 decimal places, a tenth for 1, a hundredth for 2, and so on to 4; or 1, 10, 100 or 1,000.
With Nearest, rounding 2.5 to a whole number (u = 1) gives 3.
Method & sources
You round one number at a time, either to 0–4 decimal places or to the nearest 1, 10, 100 or 1,000. Numbers are shown in the format used by the site language.
Sources
Where this method comes from — use these references to understand the formula, assumptions, and limits.
- Decimals and rounding — OpenStax, Rice University, verified 2026-09-08
- ECMAScript Math rounding methods — Ecma International, verified 2026-09-08
How we calculate
- You round one number at a time, either to 0–4 decimal places or to the nearest 1, 10, 100 or 1,000.
- Numbers are shown in the format used by the site language.
Rounding
With Nearest, a number exactly halfway between two answers goes to the higher one: 2.5 → 3 and −2.5 → −2. Round up chooses the higher result on the number line; Round down chooses the lower one. If the number already fits the chosen rounding, it does not change. The display shows up to six decimal places.
What this calculator helps with
Rounding makes a number easier to read or use. You might want a whole number for an estimate, two decimal places for a measurement, or the nearest 100 for a quick total. This calculator lets you choose the kind of rounding instead of guessing.
How to use it
- Enter the number you want to round.
- Choose decimal places and pick 0, 1, 2, 3 or 4, or choose the nearest 1, 10, 100 or 1,000.
- Choose Nearest, Round up or Round down.
- Read the rounded value, the Difference, and the two marks on the number line.
How the rounding rule works
Nearest picks the closest possible answer. If a number is exactly in the middle, it goes to the higher answer: 2.5 becomes 3, and −2.5 becomes −2. Round up chooses a higher possible value on the number line. Round down chooses a lower one. If the number already fits the chosen rounding, it stays the same.
Example
Round 3.14159 to 2 decimal places and you get 3.14. The Difference is −0.00159 because 3.14 is that much lower than the starting number. Round 1,250 to the nearest 100 and you get 1,300, with a Difference of +50.
What the result means
The main result is your new rounded number. Difference tells you what changed: it is rounded value minus original value. A plus sign means the result went up; a minus sign means it went down. The number line gives the same idea as a quick picture.
Negative numbers
Negative numbers can feel backwards at first. On a number line, −2 is higher than −3 because it is to the right and closer to zero. That is why Round up takes −2.5 to −2, while Round down takes it to −3.
Need to keep a fraction exact before rounding it? Try the fraction calculator. For percentages, use the percentage calculator. For powers, roots, and other advanced calculations, use the scientific calculator.
Common mistakes and mix-ups
- Two decimal places and the nearest 100 are different jobs. Decimal places are after the decimal point; nearest 100 changes the size of the whole number.
- Round up does not always move away from zero. For a negative number, it can move closer to zero, such as −2.5 becoming −2.
- A rounded number is simpler, not more accurate. Keep the original number when you need its full detail.
When it is useful
Use it for homework, estimates, measurements, prices, totals, or any form that asks for a certain number of decimal places. It is also handy when you want to check that a rounded answer makes sense.
FAQ
- Can I choose any number of decimal places?
- This calculator offers 0, 1, 2, 3 or 4 decimal places. For example, 3.14159 rounded to 2 decimal places is 3.14.
- What does rounding to the nearest 10 or 100 mean?
- It chooses the closest multiple of that number. For 1,234, the nearest 10 is 1,230 and the nearest 100 is 1,200.
- What happens when a number is exactly halfway?
- With Nearest, it goes to the higher result. So 2.5 becomes 3, while −2.5 becomes −2.
- How do Round up and Round down work with negative numbers?
- They follow the number line. Round up takes −2.5 to −2, which is higher; Round down takes it to −3, which is lower.
- What does Difference mean?
- It is the rounded value minus the number you entered. A positive Difference means the result is higher; a negative Difference means it is lower.
- Can I round to significant figures?
- No. This calculator only rounds to 0–4 decimal places or to the nearest 1, 10, 100 or 1,000. Significant figures use a different rule based on the first digit that is not zero.
- Can I share a calculation?
- Yes. Choose Share to copy a link that opens the calculator again with the same number and rounding choices.
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