Zerk 20 UL Daypack

Mountainsmith Zerk 20 UL Daypack is a 20L, 0.79kg1.7lb travel backpack measuring 45.7×25.4×15.2cm18×10×6in. It fits the carry-on size limit of 36 of 36 major airlines and the personal-item limit of 1 of 26. Under the seat, its 45.7cm18in side is over the 40cm15.7in limit at 12 of the 25 airlines it misses. Specs from mountainsmith.com, checked September 2026.

Volume: 20Lexpands to 23L
Weight: 0.79kg1.7lb1.7lb0.79kg
Carry-on: 36/36airlines fit it
Personal item: 1/26under-seat limits

Dimensions: 45.7×25.4×15.2cm18×10×6in 18×10×6in45.7×25.4×15.2cm
Price: $179.95 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: 38.1 to 48.3cm (15 to 19in)
Compartments: n/a
Bottle pockets: 2

Price history

$179.95 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, 840D x 100D stretch mesh, 150D polyester liner

23 L with the roll top extended; 0.7 kg stripped
Removable 1.5 in waistbelt, frame sheet and modular side compression straps
Compatible with the Zerk 7L Toplid and Zerk 3L Loki Lumbar accessories

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

Does the Mountainsmith Zerk 20 UL Daypack fit airline carry-on limits?

Draw against

Fits as a cabin bagFits as a cabin bag 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	FitsFits	Too bigToo big	6.2kg to pack (of 7kg)13.7lb to pack (of 15.4lb)
Air CanadaCabin bag not on every fare	FitsFits	Too bigToo big	No published limitNo published limit
Air FranceCabin bag not on every fare	FitsFits	Too bigToo big	11.2kg to pack (of 12kg shared with personal item)24.7lb to pack (of 26.5lb shared with personal item)
Air India	FitsFits	No published limit	6.2kg to pack (of 7kg)13.7lb to pack (of 15.4lb)
AirAsia	FitsFits	Too bigToo big	6.2kg to pack (of 7kg shared with personal item)13.7lb to pack (of 15.4lb shared with personal item)
Alaska Airlines	FitsFits	No published limit	No published limitNo published limit
Allegiant AirCabin bag not on every fare	FitsFits	Too bigToo big	No published limitNo published limit
American Airlines	FitsFits	Too bigToo big	No published limitNo published limit
ANA (All Nippon Airways)	FitsFits	Too bigToo big	9.2kg to pack (of 10kg shared with personal item)20.3lb to pack (of 22lb shared with personal item)
AviancaCabin bag not on every fare	FitsFits	No published limit	9.2kg to pack (of 10kg)20.3lb to pack (of 22lb)
British Airways	FitsFits	Too bigToo big	No published limitNo published limit
Cebu Pacific	FitsFits	Too bigToo big	9.2kg to pack (of 10kg shared with personal item)20.3lb to pack (of 22lb shared with personal item)
Delta Air Lines	FitsFits	No published limit	No published limitNo published limit
easyJetCabin bag not on every fare	FitsFits	Too bigToo big	14.2kg to pack (of 15kg)31.3lb to pack (of 33.1lb)
Emirates	FitsFits	No published limit	6.2kg to pack (of 7kg)13.7lb to pack (of 15.4lb)
Frontier AirlinesCabin bag not on every fare	FitsFits	Tight fit (0.3cm spare)Tight fit (0.1in spare)	15.1kg to pack (of 15.9kg)33.3lb to pack (of 35.1lb)
Gol Linhas Aereas	FitsFits	No published limit	9.2kg to pack (of 10kg)20.3lb to pack (of 22lb)
IndiGo	FitsFits	No published limit	6.2kg to pack (of 7kg)13.7lb to pack (of 15.4lb)
JetBlue Airways	FitsFits	Too bigToo big	No published limitNo published limit
KLMCabin bag not on every fare	FitsFits	Too bigToo big	11.2kg to pack (of 12kg shared with personal item)24.7lb to pack (of 26.5lb shared with personal item)
LATAM Airlines	FitsFits	Too bigToo big	11.2kg to pack (of 12kg)24.7lb to pack (of 26.5lb)
LufthansaCabin bag not on every fare	FitsFits	Too bigToo big	7.2kg to pack (of 8kg)15.9lb to pack (of 17.6lb)
Norwegian Air ShuttleCabin bag not on every fare	FitsFits	Too bigToo big	9.2kg to pack (of 10kg shared with personal item)20.3lb to pack (of 22lb shared with personal item)
Qantas	FitsFits	No published limit	6.2kg to pack (of 7kg shared with personal item)13.7lb to pack (of 15.4lb shared with personal item)
Qatar Airways	FitsFits	No published limit	6.2kg to pack (of 7kg)13.7lb to pack (of 15.4lb)
RyanairCabin bag not on every fare	FitsFits	Too bigToo big	9.2kg to pack (of 10kg)20.3lb to pack (of 22lb)
SAS	FitsFits	Too bigToo big	7.2kg to pack (of 8kg)15.9lb to pack (of 17.6lb)
Singapore Airlines	FitsFits	Too bigToo big	6.2kg to pack (of 7kg)13.7lb to pack (of 15.4lb)
Southwest Airlines	FitsFits	No published limit	No published limitNo published limit
Turkish Airlines	FitsFits	Too bigToo big	7.2kg to pack (of 8kg)15.9lb to pack (of 17.6lb)
United AirlinesCabin bag not on every fare	FitsFits	Too bigToo big	No published limitNo published limit
Vietjet Air	FitsFits	Too bigToo big	6.2kg to pack (of 7kg shared with personal item)13.7lb to pack (of 15.4lb shared with personal item)
VolarisCabin bag not on every fare	FitsFits	Too bigToo big	9.2kg to pack (of 10kg)20.3lb to pack (of 22lb)
VuelingCabin bag not on every fare	FitsFits	Too bigToo big	9.2kg to pack (of 10kg)20.3lb to pack (of 22lb)
WestJetCabin bag not on every fare	FitsFits	Too bigToo big	No published limitNo published limit
Wizz AirCabin bag not on every fare	FitsFits	Too bigToo big	9.2kg to pack (of 10kg)20.3lb 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 0.79kg1.7lb. Limits and sources. Own a different bag? Check it against every airline.