Please measure foot from heel to toe while standing. Then refer to size chart below (size chart picture available in cm in album)
Add 1/4-1/2" for "wiggle" room.
Size 12-18m (4) 12.6cm = 4.96 inches
Size 18-24m (5) 13.4cm = 5.27 inches
Size 6 (14.2cm) = 5.59 inches
Size 7 (15cm) = 5.9 inches
Size 8 (15.8cm) = 6.22 inches
Size 9 (16.6cm) = 6.53 inches
Size 10 (17.4cm) = 6.85 inches
Size 11 (18.2cm) = 7.16 inches
Size 12 (19cm)= 7.48 inches