A theoretical solution of natural convective heat transfer from isothermal round plates mounted vertically in unlimited space, is presented. With simplifying assumptions typical for natural heat transfer process, equations for the velocity profile in the boundary layer and the average velocity were obtained. Using this velocity, the energy how within the boundary layer was balanced and compared with the energy transferred from the surface of the vertical plate according to the Newton's law. The solution of the resulting differential equation is presented in the form of a correlation between the dimensionless Nusselt and Rayleigh numbers. The theoretical result is compared with the correlation of numerical results obtained using FLUENT. Experimental measurements of heat transfer from a heated round vertical plate 0.07 m in diameter were performed in both water and air. The theoretical, numerical, and experimental results are all in good agreement. (C) 2001 Elsevier Science Ltd. All rights reserved.