You can use expertflyer.com, and go check Flight Availability for a particular route. Within a route, it will suggest all the different options to get there. Y

You can use expertflyer.com, and go check Flight Availability for a particular route. Within a route, it will suggest all the different options to get there. You can judge at a glance how much availability there is by looking at the available seats in the fare buckets. This is for an arbitrary flight from YVR to LHR on Air Canada: J9 C9 D9 Z9 P9 R0 O8 E7 N3 Y9 B9 M9 U9 H9 Q9 V9 W9 S9 T9 L9 K9 F0 An airline splits its seats into different “buckets”, and the list above is essentially ordered from most to least expensive. J, C, D, Z, P are for business class seats. O, E, N for premium economy, and Y and beyond for economy. J9 means that there are at least 9 tickets available in the most expensive business class bucket. N3 means that there are exactly 3 tickets available in the least expensive premium economy bucket. Industry-wide, J means business class and Y means economy, but individual airlines tend to have their own fare coding within there. So with all of those nuances in mind, you can infer how full the flight is: the second least expensive business class bucket has at least 9 seats available, and the lowest one has 0, so it’s pretty quiet but not empty. Premium economy is probably 50% full. And economy seems to have a lot of space (all but the cheapest bucket have more than 9 tickets). Conversely, this is a sample of a fairly full flight (today on AC, YVR-YYZ): J0 C0 D0 Z0 P0 R0 O2 E1 N0 Y4 B8 M6 U6 H5 Q3 V2 W2 G1 S0 T0 L0 A0 K0 F0 Expert Flyer also allows you to review the seat maps for each flight you see, but of course it’s more time consuming, because then you need to click into each option. So it’s best to learn the above syntax, and then use the seat maps to validate. It’s also worth noting that the seat maps aren’t foolproof: many passengers don’t select seats until they check in (because it costs $ otherwise). Looking at the seat map for my first example above, I was able to validate that business class had 14/30 seats selected, premium economy had 12/21, and economy had ~70/~240 seats selected - lots of open space. A really good chance of having a whole block of seats to yourself. Also another interesting fact: sometimes you’ll see something like Y3 but the flight is actually sold out. This is how airlines oversell their flights. Y is the most expensive economy fare, often not too far off from a cheap business class ticket - so it’s super profitable. So the airlines will generally keep a couple extra seats available for booking on a full flight. In the best case, a few people miss connections and they’ve pocketed all of that extra money. In the worst case, they need to bump one of the lowest paying passengers and pay them off. But the payoff doesn’t cost the airline much, if anything at all, because then having to do so meant that somebody bought a super expensive ticket in their place.