As I only had 7 bed strips I decided to fit 8 boards instead of 9, I bought the wood as per
http://www.classicheartbeat.com/bed_wood.htm but when I fitted them after varnishing them I ended up with a 1 3/4" gap. I replaced one of the side planks with a 6" wide piece instead. Adding up the widths of 9 boards = 46 7/8", 8 boards = 47 1/2" & mine = 49 1/4"