Hi guys - the for,ula for quarter-square triangles is this: add 1-1-4" to the finished size of your qs block. So if you need them to finish to 4" you would add 1-14" and cut squares 5-14". Personally I need a little fudge room so I always cut mine adding 1-1/2" and when finished I square them up. You start making two half square triangles - then put them right sides together with opposite colors - mark the line from corner to corner and sew 1/4" in either side. Cut on the line and you have 2 quarter square blocks.
Hope this helps.
Sandy in Mooresville, NC