power

I left a post to this effect on your April 20th entry, Lou. Question, how tall are you? Are your legs long or short in relation to your torso. Me? I'm 5 ft 9.5 inches, proportionate legs to torso. a 14" box is parallel for me, an 18" box is about a quarter squat for me. A box squat should be harder than free squats.
 

I'm about 5 ft 7 1/2 inches tall. When I sit down on the 18 inch box. My legs are just about parallel. How can the box squats feel so much easier for me?
 

At your height, there is no way an 18 inch box squat can be parallel. I'm trying to not use my size as a reference here when I say that so the only way I could prove it to you is to ask you to pay a gym a visit or have a fellow powerlifter spot you from the side as you squat conventional. The minute you hit parallel (when your hip at the crease is below where the knees are) have him call it and try to remember how far you went. When you do the 18 inch box, you'll note that you didn't go far. That's probably why the box squats feel easier.

The other way is to go to a gym, grab an aerobic step and 14 risers (7 risers on each end is an 18" box squat, 6 is 16", 5 is 14", 4 is 12") and squat at each height and take notes.
 

I'm with Alberto on this one, Lou.
I'm 5-5 and a half and about 12" is parallel for me. Being two inches taller than me, your box should be about 14" or so.
18" is a high box squat and those should be easier than a regular squat.