AstronomyOnline.org is a comprehensive site for diagrams and models of stars, including smaller dwarf stars. Stars that appear little may actually be large stars. To best determine the actual size of a star, use a star life cycle chart, such as that found on EnchantedLearning.com.
The most highly-regarded star model is the Hertzsprung-Russell Diagram. Astronomers use this chart to help determine age and physical size of a star based on luminosity, temperature, absolute magnitude and spectral class. Once a star is identified and plotted on the Hertzsprung-Russell Diagram using at least two of the classifiers, the star's position in its life-cycle can be determined. The Hertzsprung-Russell Diagram can be found on Swinburne University's astronomy website.