and it also depends on which route you are flying. Qatar Airways is whimsical on how much it charges per kilo on excess baggage or on whether you (or the next person in line) will get charged at all.

Check their website for your routing. Better yet, fly Emirates - they allow 10kg extra (30 kg total) per bag. On a transatlantic flight for example - you can check 2 x 30kg bags - no extra cost (and no nastiness from the ground staff.

Can you tell I will never fly Qatar Airways again?