This isn't really hard to figure out.
I lied.

The sword our blockhead is holding seems to be very short, the blade is only twice as long as the hilt. From this logic we will assume it is an Arming Sword (aka Shortsword) which according to Wikipedia has a blade of about 69 centimeters (about 27 inches).
So if we put 2 sword blades on top of each other and compare them to Blockhead,

This adds up to 132 centimeters. This is 1.32 meters. Since Blockhead is 5 blocks high, this means one block would be (Rounded to the nearest 5) 0.25. This suggests that 4 blocks (Vertically) is a meter.
I feel like I've spent too much time calculating this. I wonder why.