Acetone is fragmented in two different groups, one carbonyl group and two methyl groups. For the critical volume the following calculation results: 
V = 40 + 60.0 + 2 * 55.0 = 210 cm
In the literature (such as in the Dortmund Data Bank) the values 215.90 cm, 230.5 cm  and 209.0 cm  are published.