I can’t cover all of the airlines, but I think this should give you a good idea of the average free checked luggage allowances. Presumptions: flight from USA and on an economy ticket. You can also find this on the website.
| Airline | Size | Number | Weight |
| China Southern | 20×40×55 | 1 Piece | 11 lbs |
| American Airlines | 35 inches; 45 inches | 1 Personal item; 1 Carry On | |
| United Airlines | 9x14x22 inches; 9x10x17 inches | 1 Carry On; 1 Personal Item | |
| Delta Airlines | 45 inches total | 1 Carry On; 1 Personal Item | |
| Emirates | 22 x 15 x 8 inches | 1 Personal Item | 15 lbs |
| Southwestern Airlines | 10 x 16 x 24 inches | 1 Carry On; 1 Personal Item | |
| Lufthansa | 21x15x9 inches | 1 Carry On | 17 lbs |
| Air China | 21x15x7 inches | 1 Carry On | 11 lbs |
| Air France | 21x13x9 inches | 1 Carry On; 1 Personal Item | 26.5 lbs |
| British Airways | 22x18x10 inches; 18x14x8 inches | 1 Carry On; 1 Personal Item | 50 lbs |
Student Ramblings 
That is why it is important to check with your airline first to avoid over packing.