how tall is a 72 oz ninja slushie machine

The 72 oz Ninja SLUSHi machine is about 16.93 inches tall for the 72 oz version sold at Target. Its listed overall dimensions are 16.93 in H x 6.54 in W x 16.93 in D.

If you meant the newer Twist version with two 72 oz vessels, that model is listed at 16.26 inches tall.

Quick note

The exact height can vary a little by model and retailer listing, but for the standard 72 oz unit, about 17 inches tall is the practical answer.