Semi-automatic and self-dimensioning carton sealer which seals the top and bottom of American-type variable size boxes with adhesive tape. The operator squares the boxes, folds the bottom flaps, fills the boxes, folds the top flaps, and then guides them into the machine where the centering/holding unit self-adjust to the box. Box feeding is regulated by two lateral belts. The top and the bottom flaps will be sealed simultaneously. The result is a perfect alignement of the flaps. Machine is equipped with infeed and outfeed rollers, blade to stop the box and wheels, representing a practical and simple packaging station.