As a standard fraction, 12.5 equals 25/2, or 25 halves. As a mixed fraction, it may be expressed as 12 1/2, or twelve and one-half.
To convert 12.5 to a fraction, consider the decimal portion of the number, .5. Since .5 is in the tenth spot of the decimal, it may be read as five-tenths, or 5/10. To reduce it to lowest terms, find the lowest common denominator, 5, and divide each by that number to get 1/2, or one-half. Thus, the number is now 12 1/2. To convert this mixed number into an entirely rational fraction, multiply the whole number, 12, by the denominator, 2, to get 24, then add the numerator, to end up with 25. This is the new numerator, so the rational number is 25/2. To check the work, divide 25 by 2 on a calculator or as a decimal equation, yielding 12.5.