These gel holders are made to hold one .75oz gel color holder in each cavity. 

Gel Color Holder Measurements:

Skinny – 10 Color Holder: L 5 1/4in. X W 2  3/16in.  H 1″ 3/16in

Mini – 9 Color Holder: L 3 3/16in. X W 3 3/16in. X H 1″ 3/16in

Small – 15 Color Holder: L 5 1/4in. X W 3 3/16in.  H 1″ 3/16in

Medium – 25 Color Holder: L 5 1/4in. X W 5 1/4in.  H 1″ 3/16in

Large – 30 Color Holder: L 7 7/16in. X W 5 1/3in.  H 1″ 3/16in