SturdiBag Pro (Large, Flexible Height) — dimensions & which airlines it fits
SturdiBag Pro (Large, Flexible Height): 18 × 11.5 × 11.5 in external. The flexible-height top is the whole point — it compresses down to slide under lower seats, then springs back. A common pick for the 8.5" airlines (compresses; verify for your specific seat).
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Specs
| External size (L×W×H) | 18 × 11.5 × 11.5 in |
| Type | soft-sided · flexible height |
Dimensions from the manufacturer product page · verified 2026-07-23
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Which airlines does the SturdiBag Pro (Large, Flexible Height) fit?
Compared against each airline's published under-seat limit (height strict; footprint may rotate). Green = within the published size; amber = fits only when collapsed / flexed; grey = over.
| Airline | Its limit | This carrier |
|---|---|---|
| Southwest Airlines | 18.5 × 13.5 × 8.5 in | Flexes — check height 11.5" tall vs a 8.5" limit — 3" over, but the flexible-height top compresses down. Verify it squeezes under your actual seat. |
| Frontier Airlines | 18 × 14 × 11 in | Flexes — check height 11.5" tall vs a 11" limit — 0.5" over, but the flexible-height top compresses down. Verify it squeezes under your actual seat. |
| Allegiant Air | 18 × 12 × 11 in | Flexes — check height 11.5" tall vs a 11" limit — 0.5" over, but the flexible-height top compresses down. Verify it squeezes under your actual seat. |
| Porter Airlines | 21.5 × 15.5 × 10.5 in | Flexes — check height 11.5" tall vs a 10.5" limit — 1" over, but the flexible-height top compresses down. Verify it squeezes under your actual seat. |
| Delta Air Lines | 18 × 11 × 11 in | Too big 18 × 11.5 × 11.5 in is over the 18 × 11 × 11 in limit. |
| JetBlue | 17 × 12.5 × 8.5 in | Too big 18 × 11.5 × 11.5 in is over the 17 × 12.5 × 8.5 in limit. |
| American Airlines | 18 × 11 × 11 in | Too big 18 × 11.5 × 11.5 in is over the 18 × 11 × 11 in limit. |
| United Airlines | 18 × 11 × 11 in | Too big 18 × 11.5 × 11.5 in is over the 18 × 11 × 11 in limit. |
| Alaska Airlines | 17 × 11 × 9.5 in | Too big 18 × 11.5 × 11.5 in is over the 17 × 11 × 9.5 in limit. |
| Air Canada | 17 × 16 × 8 in | Too big 18 × 11.5 × 11.5 in is over the 17 × 16 × 8 in limit. |
| Sun Country Airlines | 17 × 12 × 9 in | Too big 18 × 11.5 × 11.5 in is over the 17 × 12 × 9 in limit. |
| Hawaiian Airlines | 17 × 11 × 9.5 in | Too big 18 × 11.5 × 11.5 in is over the 17 × 11 × 9.5 in limit. |
| Breeze Airways | 17 × 8 × 13 in | Too big 18 × 11.5 × 11.5 in is over the 17 × 8 × 13 in limit. |
| WestJet | 16 × 10 × 8.5 in | Too big 18 × 11.5 × 11.5 in is over the 16 × 10 × 8.5 in limit. |
| Avelo Airlines | 17 × 9 × 13 in | Too big 18 × 11.5 × 11.5 in is over the 17 × 9 × 13 in limit. |
| Air Transat | 17 × 9.5 × 10 in | Too big 18 × 11.5 × 11.5 in is over the 17 × 9.5 × 10 in limit. |
| JSX | 17 × 13 × 11 in | Too big 18 × 11.5 × 11.5 in is over the 17 × 13 × 11 in limit. |
Compared with
SturdiBag Pro (Large, Flexible Height) vs Sherpa Original Deluxe (Large) SturdiBag Pro (Large, Flexible Height) vs Sleepypod Air SturdiBag Pro (Large, Flexible Height) vs Diggs Passenger SturdiBag Pro (Large, Flexible Height) vs Away The Pet Carrier
Not sure this is the one? See the best carriers ranked by how many airlines they fit · compare all: carriers · fit for a specific airline: Delta · JetBlue · American · United · Southwest
Common questions
What are the dimensions of the SturdiBag Pro (Large, Flexible Height)?
Its published external size is 18 × 11.5 × 11.5 in. Source: the manufacturer's product page.
Which airlines does the SturdiBag Pro (Large, Flexible Height) fit?
Against published limits it fits Southwest Airlines, Frontier Airlines, Allegiant Air, Porter Airlines. Real under-seat space varies by aircraft, so confirm for your flight.