Methods are described for quantifying an amount of natural rubber in a plant from a sample of the plant by obtaining a NMR spectrum and analyzing the signal peaks for the natural rubber in the plant sample and a standard component tested in combination with the plant sample. The NMR testing is conducted on a liquid state sample of a solution containing dissolved plant sample and standard component. A pre-determined and known amount of standard component is present in the liquid state sample and provides a reference for calculating an estimated amount of natural rubber in the plant sample. The estimated amount of natural rubber in the sample can be used to quantify the amount of extractable rubber in the sampled plant.