62 inches is the norm, and three carriers are not on it
The linear measurement — length plus width plus depth — is the number that governs a checked bag almost everywhere, and almost everywhere it is 62 inches, published as 158 cm. Three of the airlines here sit outside that. Emirates allows 150 cm on its piece-concept routes. Qantas allows only 140 cm on Australian domestic flights. Qatar allows 300 cm on weight-concept routes, which is a different rule rather than a generous one.
Delta is the odd case worth knowing about: it publishes 62 inches as 157 cm, where every other carrier prints 158. The true conversion is 157.48. Neither is wrong, but if you have a bag sitting on exactly that line, the airline you booked decides which side of it you are on.
Piece or weight is a property of the airline, not the destination
There are two systems. Under the piece concept you get a number of bags, each with its own weight cap. Under the weight concept you get a total allowance and can divide it as you like. Which one applies is decided by the carrier's own regional rules, and the carriers draw those lines differently.
Emirates and Qatar switch to pieces for the Americas and Africa. Singapore Airlines uses pieces for Canada and the USA only. Qantas uses pieces for Australian domestic and the Americas. So two people flying to the same city on different airlines can be under different systems entirely — and the allowance you remember from last time may not be the one you are on.
The weight caps that are refusals, not fees
Most weight limits are a fee. A few are a hard stop, and those are the ones worth checking before you pack. JetBlue does not accept a bag over 70 lb at all. American refuses anything over 100 lb outright. Qatar caps at 32 kg with no option above it, as do several carriers, because it is a manual-handling limit for ground staff rather than a revenue decision.
Where a cap is a refusal rather than a charge, no amount of willingness to pay helps at the desk. The bag has to be repacked there and then.
Things people ask
What does 62 inches mean?
Length plus width plus depth added together, not any single side. A bag of 30 × 20 × 12 inches is 62 linear inches.
Do wheels count?
On the airlines here that say either way, yes. The measurement is the bag at its widest point including wheels and the handle.
Why is my airline not listed?
Only airlines whose figures could be read from their own published policy are here. Two are named on the site as unverified rather than filled in from elsewhere.