Synapse 25

Tom Bihn Synapse 25 is a 25L, 0.8kg1.8lb travel backpack measuring 51×34×23cm20×13.5×9in. It fits the carry-on size limit of 30 of 36 major airlines and the personal-item limit of 0 of 26. Under the seat, its 23cm9.1in side is over the 20cm7.9in limit at 15 of the 26 airlines it misses. Specs from tombihn.com, checked September 2026.

Volume: 25Lfixed size
Weight: 0.8kg1.8lb1.8lb0.8kg
Carry-on: 30/36airlines fit it
Personal item: 0/26under-seat limits

Dimensions: 51×34×23cm20×13.5×9in 20×13.5×9in51×34×23cm
Price: $265 as of September 2026
Laptop: up to 16"
Opening: Panel access, half-zip
Warranty: Lifetime Fixes faults free of charge, wear and tear repairs are done at a reasonable charge.
Compartments: 6
Bottle pockets: 1

Price history

$265 at every weekly check since Oct 5, 2026 (3 checks).

Checked weekly on the brand's US store.

Water-resistant
Hip belt
Sternum strap
Shoulder strap

Material: 420d Spectron ripstop exterior (default), 200d Halcyon interior (bluesign/OEKO-TEX certified)

Fits a laptop up to 16" via built-in Cache-pouch attachment loops
Five exterior pockets total, including one center 32oz water-bottle pocket
Includes a Gatekeeper waist strap and sternum strap assembly
Sized to meet typical airline personal-item requirements; water-repellent YKK zippers

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

Does the Tom Bihn Synapse 25 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	6.2kg to pack (of 7kg)13.7lb to pack (of 15.4lb)
Air CanadaCabin bag not on every fare	Tight fit (no spare)Tight fit (no spare)	Too bigToo big	No published limitNo published limit
Air FranceCabin bag not on every fare	Tight fit (1cm spare)Tight fit (0.4in spare)	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	Too bigToo big	No published limit	6.2kg to pack (of 7kg)13.7lb to pack (of 15.4lb)
AirAsia	Tight fit (no spare)Tight fit (no spare)	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	Tight fit (no spare)Tight fit (no spare)	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	Tight fit (no spare)Tight fit (no spare)	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	Tight fit (1cm spare)Tight fit (0.4in spare)	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	Tight fit (no spare)Tight fit (no spare)	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	Tight fit (no spare)Tight fit (no spare)	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	Too bigToo big	No published limit	6.2kg to pack (of 7kg)13.7lb to pack (of 15.4lb)
Frontier AirlinesCabin bag not on every fare	FitsFits	Too bigToo big	15.1kg to pack (of 15.9kg)33.3lb to pack (of 35.1lb)
Gol Linhas Aereas	Tight fit (1cm spare)Tight fit (0.4in spare)	No published limit	9.2kg to pack (of 10kg)20.3lb to pack (of 22lb)
IndiGo	Tight fit (1cm spare)Tight fit (0.4in spare)	No published limit	6.2kg to pack (of 7kg)13.7lb to pack (of 15.4lb)
JetBlue Airways	Tight fit (no spare)Tight fit (no spare)	Too bigToo big	No published limitNo published limit
KLMCabin bag not on every fare	Tight fit (1cm spare)Tight fit (0.4in spare)	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	Tight fit (1cm spare)Tight fit (0.4in spare)	Too bigToo big	11.2kg to pack (of 12kg)24.7lb to pack (of 26.5lb)
LufthansaCabin bag not on every fare	Tight fit (no spare)Tight fit (no spare)	Too bigToo big	7.2kg to pack (of 8kg)15.9lb to pack (of 17.6lb)
Norwegian Air ShuttleCabin bag not on every fare	Tight fit (no spare)Tight fit (no spare)	Too bigToo big	9.2kg to pack (of 10kg shared with personal item)20.3lb to pack (of 22lb shared with personal item)
Qantas	Tight fit (no spare)Tight fit (no spare)	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	Too bigToo big	No published limit	6.2kg to pack (of 7kg)13.7lb to pack (of 15.4lb)
RyanairCabin bag not on every fare	Too bigToo big	Too bigToo big	9.2kg to pack (of 10kg)20.3lb to pack (of 22lb)
SAS	Tight fit (no spare)Tight fit (no spare)	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	Tight fit (no spare)Tight fit (no spare)	Too bigToo big	7.2kg to pack (of 8kg)15.9lb to pack (of 17.6lb)
United AirlinesCabin bag not on every fare	Tight fit (no spare)Tight fit (no spare)	Too bigToo big	No published limitNo published limit
Vietjet Air	Tight fit (no spare)Tight fit (no spare)	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	Too bigToo big	Too bigToo big	9.2kg to pack (of 10kg)20.3lb to pack (of 22lb)
WestJetCabin bag not on every fare	Tight fit (no spare)Tight fit (no spare)	Too bigToo big	No published limitNo published limit
Wizz AirCabin bag not on every fare	Tight fit (no spare)Tight fit (no spare)	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 0.8kg1.8lb. Limits and sources. Own a different bag? Check it against every airline.