This query is prompted by the fact that the online coil calculator I'm using includes heat flux and heat capacity. I believe that a twin stranded wire - e.g. a simple twist - has half the resistance of a single strand and can therefore be treated as a pair of single strand coils in parallel. However, I worked out the cross sectional area of two strands of 24g and found that it was the same as a single strand of 21g, and sure enough when I plug in the numbers for a dual coil build of single strand 24g the calculator gives very similar results to a single coil of 21g in terms of resistance and wire length, but the heat capacities are very different and the calculator predicts different voltages to achieve the same heat flux. The calculator can do multiple coils but only knows about single strand wires, so my question is if I'm making for example a single coil using a 24g twist, should I tell the calculator it's a dual 24g or a single 21g?