The question I get most often from new students is what length jian to buy, so here is the chart most schools use, plus the old way to check without a chart.
5 foot 0 and under takes a 26 inch blade.
5 foot 1 to 5 foot 6 takes a 28 inch.
5 foot 7 to 5 foot 11 takes a 30 inch.
6 foot and up...