Updated May 31, 2020 – JetBlue Airways limits you to one piece of carry-on luggage as well as one personal item on the airplane with you.
The carry on bag must not exceed 22 inches in length (55.88 cm) or 14 inches in width (35.56 cm) or 9 inches in height (22.86 cm). These size requirements include any wheels or handles that the bag may have, so take that into account when measuring the size of your carry on.
As mentioned, you can also carry a second, smaller “personal item” on the JetBlue plane with you. This bag must fit under the seat in front of you. In terms of size, that limits this personal item to no more than 17 inches in length (43.2 cm) or 13 inches in width (33 cm) or 8 inches in height, again including any wheels or handles the item may have.