Frontier 18 x 14 x 8
Delta 20 x 17 x 11 (smaller in window seat)
Air France/KLM 16 x 12 x 6
TAP Portugal 16 x 12 x 5 (max weight 4.4 lbs / 2kg)
T&L Article 20 x 17 x 11
CostCo sm bag 16 x 12 x 8 (may be thicker if stuffed full or expanded)
Fits Mult airlines 17 x 10 x 8 according to another T&L article
Conclusion: CostCo bag is legal personal item on many airlines, except Virgin and Air France/KLM/TAP Portugal,
and is only legal on United if you don't bring another carry-on
On Frontier, only the personal item is included in the fare. On TAP Portugal and Delta a personal item and a carry-on are included. Don't know about others.
For carry-on, a size of 22 x 14 x 8, max 17.5 lb, would be free on both Delta and TAP Portugal (total of 22 lbs in personal and carry-on bag on TAP)
