Math.Round Method (Double, Int32)

Updated: May 2010

Rounds a double-precision floating-point value to a specified number of fractional digits.

Namespace:  System
Assembly:  mscorlib (in mscorlib.dll)

public static double Round(
	double value,
	int digits


Type: System.Double
A double-precision floating-point number to be rounded.
Type: System.Int32
The number of fractional digits in the return value.

Return Value

Type: System.Double
The number nearest value with a number of fractional digits equal to digits.


digits is less than 0 or greater than 15.

The digits parameter specifies the number of fractional digits in the return value and ranges from 0 to 15. If digits is zero, an integer is returned.

The maximum total number of integral and fractional digits that can be returned is 15. If the rounded value contains more than 15 digits, the 15 most significant digits are returned. If the rounded value contains 15 or fewer digits, the integral digits and as many fractional digits as the digits parameter specifies are returned.

If the value of the digits in d to the right of the digits position is halfway between the digit in the digits position, that digit is rounded up if it is odd, or left unchanged if it is even. If the precision of d is less than digits, d is returned unchanged.

The behavior of this method follows IEEE Standard 754, section 4. This kind of rounding is sometimes called rounding to nearest, or banker's rounding. It minimizes rounding errors that result from consistently rounding a midpoint value in a single direction.

Notes to Callers

Because of the loss of precision that can result from representing decimal values as floating-point numbers or performing arithmetic operations on floating-point values, in some cases the Round(Double, Int32) method may not appear to round midpoint values to the nearest even value in the digits decimal position. This is illustrated in the following example, where 2.135 is rounded to 2.13 instead of 2.14. This occurs because internally the method multiplies value by 10digits, and the multiplication operation in this case suffers from a loss of precision.

The following example demonstrates rounding to nearest.

Math.Round(3.44, 1); //Returns 3.4.
Math.Round(3.45, 1); //Returns 3.4.
Math.Round(3.46, 1); //Returns 3.5.

Math.Round(4.34, 1); // Returns 4.3
Math.Round(4.35, 1); // Returns 4.4
Math.Round(4.36, 1); // Returns 4.4


Supported in: 5, 4, 3

Silverlight for Windows Phone

Supported in: Windows Phone OS 7.1, Windows Phone OS 7.0

XNA Framework

Supported in: Xbox 360, Windows Phone OS 7.0

For a list of the operating systems and browsers that are supported by Silverlight, see Supported Operating Systems and Browsers.




May 2010

Added the Notes for Callers section.

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