I imagine holding a doll-sized person in one's hands would be a bizarre experience. It's a simple thing to visualize, but the feeling of actually holding them would be another matter entirely, and it wouldn't be like holding a doll. Within your hands would be a living, breathing person moving of their own free will, their body heat warm upon your hands.
But enough about that! You guys read commentary for numbers, and I have a few for you! The fairy dolls are approximately 1:6 scale (16.67% as big) of whatever size Nanase is prior to using the spell. For most people, such a size change would result in being approximately doll sized. As such, someone who is 5 feet tall would wind up with a 10 inch doll, and someone who is 6 feet tall would wind up with a 12 inch doll. Nanase's about 5 foot 4 inches tall, resulting in a doll approximately 10.67 inches (27 cm) tall.
HOORAY FOR MATH!