The variety of the forms of fractions in the Liber Abaci might be a surprise to modern readers. Although it is not difficult to sum up the meaning of these forms, the reasons for the ‘creation’ or application of these forms are not very well studied. The author of the English translation of the Liber Abaci, Sigler, was content to suggest a reason for the usage of only one form. A fraction taking this form has an integer followed by a long fractional bar (I suggest to read the fraction from the right to left in Liber Abaci), and there are several numerators above the bar, opposite to the denominators of the same amount under the bar. I mark here this kind of fractions in the case of two pairs of numerators/denominators by “[q,p]/[n,m] + a”, which is equal to a+[(n×p+q)÷(m×n)]. According to Sigler, the choices for values of m and n might have been subjected to the measurement units concerned. Sigler gives two examples, which I sum up as follows: 2 pounds 7 soldi 3 denari in twelfth century Pisa could be written as “[3,7]/[12,20] + 2” pounds (equal to 2+[(12×7+20)÷(20×12)] pounds), since 1 pound values 20 soldi and 1 soldo values 12 denari. When the measurement units are in a decimal system, Fibonacci wrote what Sigler described as ‘decimal fractions’, such as what we find on page 93 of Boncompagni’s 1862 edition: “[3,3]/[10,10] + 18” bizantii (equal to 18+[(10×3+3)÷(10×10)] bizantii, i.e. 18.33 bizantii), which represents 18 bizantii and “[3]/[10] + 3” (i.e 3.3) miliarenses. However, this explanation does not cover all forms we encounter in the Liber Abaci and these other forms, whether more or less complex, need further, more sophisticated explanations. Moreover, Sigler’s explanation touches on only the representation of fractions. Thus, the impact of a fraction’s representation on the rules of calculation itself needs study. The present research aims to analyze the use of different forms of fractions in the Liber Abaci in the solution of the problem posed on values in measurements rather than on abstract numbers in order to reveal certain relationships between the practical facet and the theoretical facet of the knowledge on fractions presented by Fibonacci in his Liber Abaci.