In order to understand how the structural parameters of vegetable fibers influence their elastic modulus; a generalized analytical model was developed. The model, the Crystal-Fibril-Bundle theory, includes the three main factors that influence the modulus of elasticity of the fiber bundle; the microfibril angle, percentage crystallinity and cell wall volume fraction. The model is generalized and acts as a top-down and bottom-up approach that can be used to predict the modulus of any hierarchical level in any vegetable fibers. The model was verified experimentally using sisal, abaca, banana and date palm fibers, and the model results showed very high agreement with the experimental results (<10 % deviation). Further, a parametric study was conducted to simulate the effect of each structural parameter on the bundle modulus of elasticity. The Crystal-Fibril-Bundle approach provides a novel and insightful tool to understand the knockdown in elastic properties resulting from the bottom-up transition through the structural hierarchical levels of vegetable fiber. It can help natural fiber researchers estimate the fibers elastic performance without the need for intensive testing. It also helps natural fiber composite designers in developing sustainable composites with enhanced performance. This model is considered the first exhaustive model to encompass all the major structural parameters in a single model.