Rounding Calculator
How to use
- Type the number you want to round.
- Choose decimal places, the nearest 10 or 100, or significant figures, then set the amount.
- Pick a rounding mode. The result updates as you type and can be copied.
How it works
The number is handled as a decimal string, not a floating point value, so 1.005 rounded to two places gives 1.01 (half up) instead of the 1.00 many calculators show.
Half up sends a tie away from zero. Half even sends a tie to the nearest even digit, which cancels out bias over many numbers. Round up moves toward positive infinity, round down toward negative infinity, and truncate simply cuts digits off toward zero.
Significant figures count from the first non-zero digit. 0.0012345 to two significant figures is 0.0012.
FAQ
Why does 1.005 round to 1.00 in JavaScript or a spreadsheet?
Binary floating point stores 1.005 as 1.00499999999999989…, which is below the tie. This tool reads the digits you typed, so it sees an exact tie and rounds it correctly.
What is banker's rounding?
Another name for half even. 2.5 becomes 2 and 3.5 becomes 4, so ties go up and down equally often.
How do round up and round down treat negative numbers?
Round up always moves toward the larger value, so -1.231 becomes -1.23. Round down moves toward the smaller value, so -1.231 becomes -1.24. Use truncate to drop digits toward zero.
How large can the input be?
Any length of plain digits works. Scientific notation such as 1e5 is not accepted.