Planning circuits, and want to make sure I understand box fill calc.

I want to bring power into a ceiling box, and power a switched light fixture, and distribute power to 2 sets of receptacles as well. (Total of 5 Receptacles, and then the one light fixture.)

I have a Blue plastic Carlon ceiling box. Box says that it's 20 CU IN.

2008 NEC says a single 14 AWG conductor is considered 2.00 CU IN of fill.


4 CU IN for the 2 wires coming in supplying power
4 CU IN for the 2 wires going to the switch
4 CU IN for 2 wires going to one set of Receptacles
4 CU IN for the other 2 wires going to the other set of Receptacles
2 CU IN for ground wires
2 CU IN for clamps in the box? (I've seen no clear answer whether the internal clamps in plastic boxes are considered clamps in box fill. So I assume they are counted to be on the safe side.)

From what I understand, the 2 wires for the light fixture are not counted because they originate and terminate within the box.

So, with all that in mind, that adds up to a 20 CU IN fill, which is the max this box is rated for.

Is this correct?