Explanation for פרק ד הלכה ד: One Kor = 30 Se'ah. One Se'ah = 2,500 square Amos, times 30 = 75,000 square Amos. One Kor = 75,000 square Amos. The Rambam rounds up the square root of 75,000 to 274 (real number is almost equal 273.8)