If you are travelling on Qatarairways the ammount allowed as check in bagagge as well as on board will depend on the "class" you are using to fly (economy, business, first). If it's QA check here

http://www.qatarairways.com/qa/en/baggage.html

Any other airliner will have its own rules so better check with them instead of the public forum.

Regards!!