Rounding in Results

Melissa was having a hard time understanding why Excel displays certain numbers in certain ways. She provided, as an example, the following steps:

1. Start with a new, blank worksheet.
2. In cell B2, enter 33.33333333.
3. In cell B3, enter 33.333333333 (one more digit than in step 2).
4. In cell C2, enter =B2*3.
5. In cell C3, enter =B3*3.

When Melissa would do this, cell C2 would display the result as 99.99999999, and cell C3 would display the result as 100.

To understand why Excel does this, there are a few things you have to understand. First of all, when you create a new worksheet, all the cells are formatted using the General format. Using this format, information is displayed in a general manner (thus the format name). In this format, numbers are displayed using up to ten digits. It doesn't matter whether the digits are to the left or right of the decimal place; only a maximum of ten are displayed.

What happens if the number that you are entering has more than ten digits, or if the result of a formula has more than ten digits? Then Excel rounds the number so that no more than ten digits are displayed. Thus, 99.99999999 is displayed, but if you add one more digit, the rounded result is 100. Rest assured, however, that Excel continues to maintain the cell contents with fifteen digits of accuracy, even though fewer digits are displayed.

If the number you are entering contains nothing to the right of the decimal point, but there are more than ten digits in the number, then the General format results in the number being displayed using scientific notation.

There is one caveat to the above: if the General-formatted cell into which the value is placed is narrower than what is required to display the full number, then the value is rounded so that it can be displayed within the available column width. If you later adjust the column width so it is wider, then the number is reformatted so it is displayed with up to ten digits.

If you want to use more than ten digits to display your number, you need to explicitly format the cell. Either click on the Increase Decimal tool on the Formatting toolbar, or choose Format | Cells and use the Number tab to control how the displayed number should be formatted.