2 feats for 2 different characters, so lets start
Density of human bones is around 1.7500 g/cm^3. Since both feat is based on busting of skeleton, this will be common.
Asakura Yoh busts a skeleton []
Mass of the sketon: 1273 kg
Putting the values in this density calculator, the volume of the skeleton would be 727428.57142857 cubic centimeter
From the look of the feat, it looks like fragmentation
727428.57142857 * 8 = 5819428.57142856 Joules or 1.4 Kilojoules of TNT - Wall level
Ren Tao busts the skeleton []
Same feat, but on a larger scale. This time mass of the skeleton is 12730 kg
Volume I got this time is 7274285.7142857 cubic centimeter
Looks like I should use pulverization value for this
7274285.7142857 * 214.35 =1559243142.857139795 Joules or 0.37 tons of TNT - Building level