Do you mean the Lin Similarity? It scales between 0 and 1 and is computed as following (citing the NLTK documentation):
Lin Similarity: Return a score denoting how similar two word senses are, based on the Information Content (IC) of the Least Common Subsumer (most specific ancestor node) and that of the two input Synsets. The relationship is given by the equation 2 * IC(lcs) / (IC(s1) + IC(s2)).
>>> dog.lin_similarity(cat, semcor_ic) 0.88632886280862277
You can find a comparison between different word similarity measurements in this paper. It explains the Lin Similarity as follows:
The lin and jcn measures augment the information content of the LCS with the sum of the information content of concepts A and B themselves. The lin measure scales the information content of the LCS by this sum, while jcn takes the difference of this sum and the information content of the LCS.