I have a trip to Thailand in February.
Have booked a couple of flights within the country, one on a LCC.
The standard for the domestic market appears to be 7 km for all your cabin baggage, including personal item.
Will be interesting to see how they enforce on these short flights.
Supposedly they will force you to check but I thought they couldn't put anything with lithium batteries in the cargo hold.
Our experience, after six winters in SE Asia and lots of LCC air in Thailand, Vietnam, and Malaysia is that they do indeed enforce them. Some to the letter, others sporadically. Seems to depend on the airport and the carrier. Air Asia, NOK, Jetstar, Scoot, Lion etc. Our flights were typically 1 - 1.5 hrs. Since retiring we have done more AirAsia flights that we have on some domestic carriers.
Very few seem to include the weight the personal item (purse, etc) with the carry on limit. Last time that happened to us was on a Hong Kong Airlines flight from Bangkok.
If I am not certain I place some heavier itens in a jacket pocket. That is good for 1KG for that does not get weighed! We had a Jetstar flight from Brisbane. Our bag was weighed at check in AND again by an agent in the boarding area!
As an example, on our last Air Asia flight from Kuala Lumper to Krabi, Thailand, Air Asia agents were weighing luggage prior to passengers going through security at the AirAsia section of KUL.
We believe that they do give you some leeway on weight...about 1KG. Keep in mind that the carry dimensions are also slightly smaller than the NA dimensions. A carry on label on bag in a luggage store is meaningless. Same in Europe. It is why we switched to a slightly smaller international carry on roller bag.
You will see, as we have, a huge difference in boarding in SE Asia. Same in Europe on LC airlines and in Australia. We only see the carry on boarding disaster in North America...US and Canada.