Measure distance between side and divider and subtract 1”.
Per drawer, cut two – 1x12 to this length (front and back of drawer).
Cut two 1x12 to 20-1/2” long per drawer (drawer sides). Drill three 3/4” pocket holes on each end of drawer sides. Attach drawer sides to drawer front/backs with 1-1/4” pocket hole screws.
Measure bottom of drawer and cut 1/4” plywood to fit. Use 3/4” brad nails and glue to attach.