Which airlines allow a 17 × 10 × 9 in personal item?

It fits the under-seat limit on 4 of the 21 airlines that publish one: United, Sun Country, Avelo and Qantas. It’s too big for American (1 in too deep), JetBlue (1 in too deep), Frontier (1 in too deep), Allegiant (1 in too deep), Breeze (1 in too deep), Ryanair (1.3 in too tall), easyJet (1.1 in too deep), British Airways (3 in too deep), Wizz Air (1.3 in too tall), Jet2 (1.3 in too tall), AirAsia (5.1 in too deep), Malaysia Airlines (2.8 in too tall), Singapore Airlines (5.1 in too deep), Scoot (5.1 in too deep), Air Canada (2.7 in too deep), WestJet (3 in too deep) and Virgin Australia (1.1 in too deep). Delta, Southwest, Alaska, Hawaiian, Batik Air, Cathay Pacific and Jetstar give no size: it just has to fit under the seat in front of you.

It fits the carry-on limit on 27 of 28 airlines: American, Delta, United, Southwest, JetBlue, Alaska, Frontier, Allegiant, Hawaiian, Sun Country, Breeze, Avelo, easyJet, British Airways, Wizz Air, Jet2, AirAsia, Malaysia Airlines, Batik Air, Singapore Airlines, Scoot, Cathay Pacific, Air Canada, WestJet, Jetstar, Qantas and Virgin Australia. It’s too big for Ryanair (1.1 in too deep).

Free in every fare on American, Delta, United, Southwest, JetBlue, Alaska, Hawaiian, Sun Country, Avelo, British Airways, Jet2, AirAsia, Malaysia Airlines, Batik Air, Singapore Airlines, Scoot, Cathay Pacific, Jetstar, Qantas and Virgin Australia. Free except in the cheapest fare on Air Canada (Economy Basic) and WestJet (UltraBasic). On Frontier, Allegiant, Breeze, easyJet and Wizz Air it’s a paid cabin bag: only a smaller under-seat bag is free. On Ryanair it’s too big for the cabin and would have to be checked.