Weight of A Bag for Flight Journey

I live in Spain and originally I am from India. 

I travel annually 2 times to and fro journey in any airline, now a days in Etihad Airways, between India and Spain. 

 

In India I have to do a domestic flight journey also to reach my city.

 

Thus, I have one international journey and one domestic journey. 

 

Two different airways I use for these journeys. 

Weight allowed by Domestic airlines 

 

Domestic airline allows me to carry only 15 kg in a check-in bag and 7 kg in a hand bag. 

 

Additionally, I can carry a laptop bag for my laptop. 

 

Airline allows Maximum weight of laptop bag is 3 kg. 

Weight allowed by International airlines 

 

International airline allows me to carry only 31-35 kg in a check-in bag and 7 kg in a hand bag. 

 

Additionally, I can carry a laptop bag for my laptop. 

My question 

 

I do first domestic journey to reach to a international airport. 

According to rule I only can carry 15 kg in my domestic check-in bag although the rule allows me to carry 31-35 kg in international check-in. 

Due to this limitation of domestic flights, I am only able to carry 15 kg weight in check-in bag for international flight. 

Nevertheless, I saw people carrying 2-3 big bags at international airport. 

Solution 

I discussed this issue with two airline representatives when I was collecting my boarding pass for my international journey. 

They informed me that I have to look whether airline provide me:

 

31 kg per piece check-in bag? 

 

31 kg total weight in check-in bag? 

I have to give special focus on "per piece bag" and "total weight". 

If it is "total weight", in this case, I can carry 2-3 bags but total weight of bags must be 31 kg. 

That's why I saw people carrying 2-3 bags. 

Beyond this weight limit airline will charge me. 

Domestic airline allows per piece weight for check-in bag. 

Therefore, I can carry only one check-in bag of 15 kg. 

Beyond this limit, domestic airline charge me 550 RS per extra kg of weight in my check-in bag. 

However, airline people suggested me to do a pre-booking of 1 extra bag to carry more than 15 kg weight for your domestic flight. 

This will be much cheaper than paying money for each extra kg at the domestic check-in counter. 

There is no problem with International check-in because 31 kg weigh in 2-3 bags is allowed for check-in by the rule and regulations of aviation authorities.