After reading Mustlovedogs' thread about standardizing carry-on baggage, I was curious about TAROM, which is a Romanian airline I will be flying later this year. For being such a small airline, they were amazing precise about their requirements. If they are flying a codeshare flight (which they are on my first flight to Bucharest from AMS), then the originating airline's rules apply. If it's a separate flight (like my later flight from Bucharest to Budapest), they list their own requirements.
They also included a handy link to a carry-on calculator, where you can plug in your airline and see what the requirements are. The few that I checked were accurate. Keep in mind, this is for SkyTeam airlines only, which includes Delta, KLM, Air France and about 15 other major airlines. https://www.skyteam.com/en/hand-luggage-policy?type=luggage&airlineList=KL-Y
StarAlliance, which is another one of the 3 major airline alliances, has something similar for its airlines, which includes United. Lufthansa, and about 23 other major airlines: https://www.staralliance.com/en/baggage-information
Unfortunately, OneWorld, which includes American, Alaska and British Airways, does not have a calculator, although many of the individual airlines do.