How tall are your speaker stands

Timrhu is right, it depends on the speakers.

Generally speaking, I like tweeters to be above my ear level. This usually produces a more spacious sound minus the brightness. Another advantage is higher off the floor and clean up the bass even more.

But there are exceptions. My large speakers sound better with my ears at tweeter level.

I agree 100% with member Entrope. If anything you can always
change out the listening chair/couche(s) if needed. In my case the stands cost a lot more than the chair did! LOL
BTW- get an adjustable type stand 20-24" should do the job nicely.

Tall enough to reach the ground.

There are many full range speakers with tweeters positioned higher than the ears level. Also, in many live performance in small rooms, the singer's voice would come above the ears level when you sit in a chair.
So, I am not sure how accurate the general rule (tweeter height == ears level) is. But, you may not have it so higher or lower than the listening level. ;-)