This is a one size fits most, but fits anywhere from a 19-23” head. It fits everyone in my family, from my 3 y/o to my husband.

The 20 sts and 26 rows (4” x 4” gauge) was for US 7 needles.
The US 8 needles had an 18 sts and 24 rows (4” x 4” in stockinette) gauge for me.