An experimental investigation of transitional natural convection in an air filled cube was conducted in this research. The characteristic dimension of the enclosure is 0.35 m, and data were collected in the middle plane of the cavity. The Rayleigh number range examined is . This was achieved by varying the temperature on the hot and cold walls. The velocity field in the middle plane is measured using particle image velocimetry (PIV). Temperature measurements in the core of the enclosure indicate a linear profile. The average Nu number is also presented and compared against other correlations in the literature. This study attempts to close the gap of available experimental data in literature and provide experimental benchmark data that can be used to validate computational fluid dynamics (CFD) codes since the estimated error from PIV measurements is within 1–2%.