Would probably work better if you pretend You don’t actually now the numbers but instead compare it something else.

“I dunno, about as tall as my aunts big fridge”

(Which in this example is a double door and therefor big but shorter then most tall friged)

Or. Tall enough to reach things standing on top of my closet.

You don’t need to lie, just find something that is hard to reference but sounds tall.

Anyway, i find peoples obsession with Height in romance incredibly strange.