Hot tearing severity was evaluated in this experiment by introducing a new apparatus called Constrained Rod Casting Modified Horizontal (CRCM-Horizontal). Six constraint bars with different lengths can produce hot tearing on the cast sample. Mold position was modified from vertical to horizontal and the shape was changed from a harp shape to a star shape, which allows for the liquid metal to feed into each rod cavity simultaneously. Hot tearing development was recorded along the bars by a digital camera. A new Hot Tearing Susceptibility (HTS) formula was developed for quantitative investigation of hot tearing on a cast sample. The parameters of the HTS formula are bar length of cast sample (Li), tear severity (Ci) and location of hot tear (Pi). Footprint charts and hot tear scales are used to illustrate hot tearing severity. The experiment was conducted with Al-1.36Zn-1.19Si and Al-5.9Cu-1.9Mg alloys to investigate the sensibility of the apparatus and modification its operation.