see wikipedia on the subject:
In mathematics, specifically algebra, a conversion factor is used to convert a measured quantity to a different unit of measure without changing the relative amount. To accomplish this, a ratio (fraction) is established that equals one (1). In the ratio, the conversion factor is a multiplier that, when applied to the larger unit, converts the larger unit into the smaller unit, by multiplication with the measured amount.
24 hrs/1 day = 1 or 43,560 square feet/1 acre = 1
3 days = 3 × 24 hours = 72 hours (conversion factor is 24)
Note: If a=b, then a/b=1 and b/a=1
Days are converted, to hours, by multiplying the days by the conversion factor as 24. The conversion can be reversed by dividing, the hours, by 24 to get days; however, the reciprocal 1/24 could be considered the reverse conversion factor for an hours-to-days conversion, where 1/24 ~= 0.0416666666667. Hence, the term "conversion factor" is the multiplier which yields the result, not a divisor from that viewpoint. To yield hours, the conversion factor is 24, not 1/24, so: hours = days × 24 (multiplying by the factor).
https://secure.wikimedia.org/wikipedia/en/wiki/Conversion_factor
..or be lazy and use this software to convert measurements:
http://joshmadison.com/convert-for-windows/
...(if you put 1 in the box then the other value will be the conversion factor)