You can download all the SRAM manuals online. For the SRAM force 1 groupset, SRAM provides a precise procedure for sizing the chain: you wrap the chain directly around the single front chain ring and the largest rear cog (not through the RD) and then you basically add two internal and two external links. The manual provides pictures of all of this.

On my bike as it arrived from Bikes Direct my chain was a full two links two short – I basically had one internal link and one external link of overlap.

I had suspected it might be too short because when in the biggest rear cog the derailleur was just about being ripped off the bike.