Mishnah Berurah — משנה ברורה

If the majority is open, it is obligated - This is specifically the majority of the whole garment. And not like the way that the tailors make a טלית קטן, where they sew it up on the sides and leave over holes [on each side] where one puts his hands through... and they sew it below the hole and leave the majority open, and they measure it only from under the [hole for the] hands/arms. And this is a complete error, for then it is not called a four cornered [garment]. And it's close to [a situation] where the person blessing is making a blessing in vain. And in any case, it is no better than a garment with [exactly] half [the sides] open, which is obligated in ציצית, but is forbidden to bless on it and is forbidden to go out with it on Shabbos. So instead, one needs to measure even from what's above the [holes for the] hands, and the hole is considered also as if it's closed. And see [further] in Biur Halacha.