🎯Rounding Calculator

About this tool

Type a number, then choose whether to round to decimal places, significant figures or the nearest multiple, such as 5, 0.25 or 100. The main result uses ordinary school rounding, and a table shows the answer under every other rule, so you can match a spreadsheet, a programming language or an exam board.

Rounding rules explained

Rounding keeps a number to a chosen precision. To round 2.345 to two decimal places, look at the next digit: it's 5, so round up to 2.35. To round 0.004567 to two significant figures, count from the first non-zero digit to get 0.0046. To round 17 to the nearest 5, pick the closer multiple, 15. Rounding rules only disagree in two situations: exact halves, and when you always want to go one way. Schools round halves away from zero, so 2.5 becomes 3 and −2.5 becomes −3. "Half up" sends halves towards positive infinity, so −2.5 becomes −2. Banker's rounding (half to even) sends halves to the nearest even digit: 2.5 becomes 2 and 3.5 becomes 4. Because it rounds up and down equally often, it avoids building up bias in large totals, and it's the default in Python, .NET and IEEE-754 arithmetic. Ceiling always goes up, which is what you want for "how many boxes do I need?". Floor always goes down, and truncation just cuts the digits off. Honest limits: computers store most decimals in binary, so a typed 2.345 is really 2.34499999…. The tool compensates for this, but some spreadsheets don't, which explains occasional surprises. The significant figures calculator, the scientific notation converter and the IEEE-754 converter are related.

Frequently asked questions