Natural convection heat transfer from fin arrays was investigated experimentally at a wide range of Rayleigh numbers for fin height and different tip-to-base fin spacing ratios (C=S-t/S-b). Base fin spacing, fin length and fin thickness were kept fixed at 12, 100 and 3 mm respectively. The ratio C was varied from 0.25 to 1 and fin height was also varied from 15 to 40 mm. It was found that the convection heat transfer rate from fin array takes on a maximum value as a function of the C and fin height for a given temperature difference between fin arrays and surrounding. The results obtained from experimental study showed that the optimum C which yields the maximum heat transfer rate is between C=0.50 and C=0.75. The optimum ratio also depends strongly on the fin height and Rayleigh number. It was observed that fin arrays with an optimum ratio gave higher Nusselt numbers compared to rectangular shaped fin arrays. The increase in the Nusselt number was determined to be about 33%. An empirical correlation for the Nusselt number was derived in the result of experimental study.