The total permitted weight for two (2) pieces must not exceed 7 kg.
My carry-on bag on the way here had plenty of print materials and was more than 20 kg, more than the hold luggage :)
(One optimised for weight, and one optimised for size)
Now the paperwork is gone, but some of the weight remains. Do they weigh bags?
Once in Puerto Rico I saw people being weighted on a scale before boarding a plane.
I'm not talking about bags, I'm talking about people!
China is generally strict.
The weight of each carried item must not exceed 5 kg (11 lbs.), and the volume must not exceed 20×40×55 cm.
I was lucky enough that some of my friends were travelling by train - I asked them to take some stuff for me while I followed regulation religiously.
I saw so many other people with way larger (and supposedly much heavier) luggage. But I did not notice any weighing device.