HTML and CSS Reference
Figure 9.24 The Math object, some properties and methods.
There are three Math methods available for rounding numbers up or down. They are the
ceil() , floor() , and round() methods (see Table 9.7 for examples). The differences among the
methods might be confusing because all three methods truncate the numbers after the dec-
function, but this function truncates the number after the decimal point, without rounding
either up or down.
The ceil() Method. The ceil() method rounds a number up to the next largest whole
number and then removes any numbers after the decimal point; thus, 5.02 becomes 6
because 6 is the next largest number, and -5.02 becomes -5 because -5 is larger than -6.
The floor() Method. The floor() method rounds a number down to the next lowest
whole number and then removes any numbers after the decimal point; thus, 5.02 now
becomes 5, and -5.02 becomes -6.
The round() Method. The round() method rounds up only if the decimal part of the
number is .5 or greater. Otherwise, it rounds down to the nearest integer; thus, 5.5 is
rounded up to 6, and 5.4 is rounded down to 5.
Table 9.7 Rounding up and down