Hello ladies 
The two squares patterns I used were the Flowers in the Snow pattern from Ravelry, and Summer Garden square from Attic24.
Neither comes up to 6", so I just made up some borders.
I think I found that a row of Uk trebles / US dc is about 0.5", so a border adds 1".
It was a good opportunity for me to try out some new stitches, being a beginner. Turning corners I just did 3 or 5 stitches into the previous corner stitch. Adding borders also stabilises the square and makes it less holey / floppy if the centre is mostly granny clusters.