Zerk 55 UL Backpack

Mountainsmith Zerk 55 UL Backpack is a 53L, 1.59kg3.5lb travel backpack measuring 61×27.9×22.9cm24×11×9in. It fits the carry-on size limit of 3 of 36 major airlines and the personal-item limit of 0 of 26. Under the seat, its 22.9cm9in side is over the 20cm7.9in limit at 15 of the 26 airlines it misses. Specs from mountainsmith.com, checked September 2026.

Volume: 53Lexpands to 58L
Weight: 1.59kg3.5lb3.5lb1.59kg
Carry-on: 3/36airlines fit it
Personal item: 0/26under-seat limits

Dimensions: 61×27.9×22.9cm24×11×9in 24×11×9in61×27.9×22.9cm
Price: $279.95 as of September 2026
Laptop: no laptop sleeve
Opening: Roll-top, Roll top closure with V-strap compression
Warranty: Lifetime Covers material and workmanship defects, abuse and natural material aging may not be repairable.
Torso length: 40.6 to 55.9cm (16 to 22in)
Sizes: MD, LG
Compartments: n/a
Bottle pockets: 2

Price history

$279.95 at every weekly check since Oct 5, 2026 (3 checks).

Checked weekly on the brand's US store.

Hydration sleeve
Frame sheet (removable)
Hip belt (removable)
Sternum strap

Material: 210D and 100D Robic nylon X-Grid Extreema (UHMWPE) ripstop with UTS coating, Spundura stretch mesh, 150D polyester liner

Listed as 55L but Mountainsmith publishes 53 L, or 58 L with the roll top extended
MD fits 16 to 20 in torsos, LG 18 to 22 in
Removable padded waistbelt with two zip pockets, removable frame sheet

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Last checked: 2026-09. Prices and specs may have changed.

Does the Mountainsmith Zerk 55 UL Backpack fit airline carry-on limits?

Draw against

Too bigToo big on Ryanair. cabin bag 55×40×20cm21.5×15.5×8in · under the seat 40×30×20cm15.5×12×8in. Bag in cminches, turned to fit.

Flag as a tight fit undercm spare

Airline	Carry-on	Personal item	Cabin-bag weight
Air Arabia	Too bigToo big	Too bigToo big	5.4kg to pack (of 7kg)11.9lb to pack (of 15.4lb)
Air CanadaCabin bag not on every fare	Too bigToo big	Too bigToo big	No published limitNo published limit
Air FranceCabin bag not on every fare	Too bigToo big	Too bigToo big	10.4kg to pack (of 12kg shared with personal item)22.9lb to pack (of 26.5lb shared with personal item)
Air India	Too bigToo big	No published limit	5.4kg to pack (of 7kg)11.9lb to pack (of 15.4lb)
AirAsia	Too bigToo big	Too bigToo big	5.4kg to pack (of 7kg shared with personal item)11.9lb to pack (of 15.4lb shared with personal item)
Alaska Airlines	Too bigToo big	No published limit	No published limitNo published limit
Allegiant AirCabin bag not on every fare	Too bigToo big	Too bigToo big	No published limitNo published limit
American Airlines	Too bigToo big	Too bigToo big	No published limitNo published limit
ANA (All Nippon Airways)	Too bigToo big	Too bigToo big	8.4kg to pack (of 10kg shared with personal item)18.5lb to pack (of 22lb shared with personal item)
AviancaCabin bag not on every fare	Too bigToo big	No published limit	8.4kg to pack (of 10kg)18.5lb to pack (of 22lb)
British Airways	Too bigToo big	Too bigToo big	No published limitNo published limit
Cebu Pacific	Too bigToo big	Too bigToo big	8.4kg to pack (of 10kg shared with personal item)18.5lb to pack (of 22lb shared with personal item)
Delta Air Lines	Too bigToo big	No published limit	No published limitNo published limit
easyJetCabin bag not on every fare	Too bigToo big	Too bigToo big	13.4kg to pack (of 15kg)29.5lb to pack (of 33.1lb)
Emirates	Too bigToo big	No published limit	5.4kg to pack (of 7kg)11.9lb to pack (of 15.4lb)
Frontier AirlinesCabin bag not on every fare	Tight fit (no spare)Tight fit (no spare)	Too bigToo big	14.3kg to pack (of 15.9kg)31.5lb to pack (of 35.1lb)
Gol Linhas Aereas	Too bigToo big	No published limit	8.4kg to pack (of 10kg)18.5lb to pack (of 22lb)
IndiGo	Too bigToo big	No published limit	5.4kg to pack (of 7kg)11.9lb to pack (of 15.4lb)
JetBlue Airways	Too bigToo big	Too bigToo big	No published limitNo published limit
KLMCabin bag not on every fare	Too bigToo big	Too bigToo big	10.4kg to pack (of 12kg shared with personal item)22.9lb to pack (of 26.5lb shared with personal item)
LATAM Airlines	Too bigToo big	Too bigToo big	10.4kg to pack (of 12kg)22.9lb to pack (of 26.5lb)
LufthansaCabin bag not on every fare	Too bigToo big	Too bigToo big	6.4kg to pack (of 8kg)14.1lb to pack (of 17.6lb)
Norwegian Air ShuttleCabin bag not on every fare	Too bigToo big	Too bigToo big	8.4kg to pack (of 10kg shared with personal item)18.5lb to pack (of 22lb shared with personal item)
Qantas	Too bigToo big	No published limit	5.4kg to pack (of 7kg shared with personal item)11.9lb to pack (of 15.4lb shared with personal item)
Qatar Airways	Too bigToo big	No published limit	5.4kg to pack (of 7kg)11.9lb to pack (of 15.4lb)
RyanairCabin bag not on every fare	Too bigToo big	Too bigToo big	8.4kg to pack (of 10kg)18.5lb to pack (of 22lb)
SAS	Too bigToo big	Too bigToo big	6.4kg to pack (of 8kg)14.1lb to pack (of 17.6lb)
Singapore Airlines	FitsFits	Too bigToo big	5.4kg to pack (of 7kg)11.9lb to pack (of 15.4lb)
Southwest Airlines	Tight fit (no spare)Tight fit (no spare)	No published limit	No published limitNo published limit
Turkish Airlines	Too bigToo big	Too bigToo big	6.4kg to pack (of 8kg)14.1lb to pack (of 17.6lb)
United AirlinesCabin bag not on every fare	Too bigToo big	Too bigToo big	No published limitNo published limit
Vietjet Air	Too bigToo big	Too bigToo big	5.4kg to pack (of 7kg shared with personal item)11.9lb to pack (of 15.4lb shared with personal item)
VolarisCabin bag not on every fare	Too bigToo big	Too bigToo big	8.4kg to pack (of 10kg)18.5lb to pack (of 22lb)
VuelingCabin bag not on every fare	Too bigToo big	Too bigToo big	8.4kg to pack (of 10kg)18.5lb to pack (of 22lb)
WestJetCabin bag not on every fare	Too bigToo big	Too bigToo big	No published limitNo published limit
Wizz AirCabin bag not on every fare	Too bigToo big	Too bigToo big	8.4kg to pack (of 10kg)18.5lb to pack (of 22lb)

Compared in any orientation against each airline's published size limit. A tight fit has under 2cm to spare, so a packed soft bag may not pass a sizer. Set it to 0 to turn the warning off. Weight is what the airline allows in the cabin minus this bag's empty 1.59kg3.5lb. Limits and sources. Own a different bag? Check it against every airline.