The standard carry-on baggage size is 22 x 14 x 9 inches (56 x 36 x 23 cm) including wheels and handles. In linear measurement, that is 45 linear inches total.
This size was designed to fit overhead bins on commercial aircraft. Luggage brands including Samsonite, Travelpro, Briggs & Riley, and Away all use this standard.
Variations exist. Southwest Airlines allows 24 x 16 x 10 inches, the most generous major airline policy. Most international airlines accept the 22 x 14 x 9 standard but some weight-limit their carry-ons to 7 kg (about 15 pounds).
Hard-sided spinner cases with 4 wheels often measure an inch larger than the label claims. Soft-sided bags usually fit as marked.
See: size limits by airline.