Rounding Calculator
Round any number to decimal places, significant figures or the nearest integer — with the deciding digit highlighted every time.
Step by step calculations
Enter a number, choose a mode and press Round
The rounding rule
Look at the digit immediately after your chosen position. That is the deciding digit.
Rounding Calculator Explained
Core concepts, classroom applications, and plain-English explanations for all audiences.
Rounding is everywhere, not a shortcut
Every price you see has been rounded: £3.49 not £3.4942. Every statistic in a news report is rounded: "unemployment at 4.2%", not "4.2381742%". Every measurement you take with a ruler is rounded to the nearest millimetre. Rounding isn't dumbing down — it's making numbers usable.
Worked example
"A plank is measured as 2.347 metres. Round to 2 decimal places for the order form."
2.347 → look at the 3rd decimal: 7
7 ≥ 5 → round up the 2nd decimal
4 → becomes 5
Result: 2.35 metres
The deciding digit (7) is immediately after your chosen position. Always look at exactly one digit further right.
Decimal places vs significant figures
- → Decimal places: Count from the decimal point. 3.476 to 2dp = 3.48
- → Significant figures: Count from the first non-zero digit. 0.004762 to 2sf = 0.0048
Rounding errors can compound
If you round at each step of a calculation, errors stack up. In science and finance, it's standard to keep full precision throughout and only round the final answer.
What is Rounding?
Rounding is a way of simplifying numbers to make them easier to work with or understand, while keeping them close to their original value. It's like estimating, but with a specific set of rules.
We use rounding in everyday life, from estimating costs to reporting statistics. In maths, it's crucial for approximating answers, especially when dealing with long decimals or very large numbers. This calculator helps you round numbers to decimal places, significant figures, or the nearest whole number, 10, 100, or 1000.
Rounding rules to remember
To round a number, you need to identify the 'deciding digit'. This is the digit immediately to the right of the place you are rounding to.
If you're rounding to 1 decimal place, the deciding digit is the second decimal place.
If the deciding digit is 5 or more (5, 6, 7, 8, 9), you round up. This means you increase the digit in the place you're rounding to by one.
Rounding 3.47 to 1 decimal place: The deciding digit is 7 (which is 5 or more), so we round up the 4 to 5. Result: 3.5
If the deciding digit is 4 or less (0, 1, 2, 3, 4), you round down. This means the digit in the place you're rounding to stays the same.
Rounding 3.42 to 1 decimal place: The deciding digit is 2 (which is 4 or less), so the 4 stays the same. Result: 3.4
Common mistakes to avoid
- Rounding 3.449 to 1 decimal place as 3.5:You should only look at the digit immediately after the place you're rounding to. Don't round in stages (e.g., rounding 3.449 to 3.45 first, then to 3.5). 3.449 rounded to 1 decimal place is 3.4 (because the second decimal place is 4, so you round down).
- Rounding 2345 to 2 significant figures as 23:When rounding large numbers to significant figures, you must maintain the place value by adding zeros at the end. Otherwise, you change the magnitude of the number completely. 2345 rounded to 2 significant figures is 2300 (the 4 is the deciding digit, so the 3 stays the same, and the remaining digits are replaced with zeros).