The easiest way is to go out and measure your gate diagonally and then find the size of the True Latch gate brace that will work within the diagonal dimension of your gate.  Here are the brace sizes and dimensions that they will extend from and up to: 64" Original: 64" exactly  6' Telescopic : 40" up to 72" 8" Telescopic : 52" up to 96" 9' Telescopic : 64' up to 108" 10' Telescopic : 64" up to 120"