In the majority of structural concrete design, the compressive strength is obtained from testing of 150x300 mm concrete cylinders under standard laboratory controlled conditions with different capping system. Some testing machines are unable to produce the force needed to break high-strength 150x300 mm concrete cylinders. If 100x200 mm cylinders are to be used in quality assurance testing, the relationship between fc4 and fc6 needs to be understood in order to ensure that concrete with sufficient strength is provided. 100x200 mm cylinders are lighter and can easily be handled, collection of quality control and assurance specimens would be easier for contractors and inspectors. This research work was born from the need to determine a correlation between the strength of the standard size 150x300 mm and 100x200 mm cylindrical specimen. A total 72 no. of 100x200 mm and 150x300 mm cylinders were tested according to ASTM. Cylinders prepared by sand and sulfur capping reveals a little difference in the strength level, 150x300 mm and 100x200 mm sulfur capped cylinders shows 23% and 21% higher strength than sand capped cylinders and 100x200 mm cylinder gives 39% higher strength than 150x300 mm cylinder.