In neuroscience, the g-ratio is the ratio of the inner diameter of an axon to the total outer diameter, says PubMed. It is used to determine the optimal level of myelination in the axon of a nerve.
The g-ratio is commonly used during peripheral nerve regeneration, according to PubMed. The ratio is an indicator of the speed at which the nerve fibers conduct impulses, providing information as to how effectively a nerve is functioning. Theoretically, the optimal g-ratio of a nerve is 0.6, but researchers are finding that optimal g-ratios vary for a nerve depending on which part of the nervous system it belongs.