Hi, Is it true that girls can't wear sleeveless shirts/dress in Grand Palace and the other temples in Bangkok?

How long should the skirt be if we'll be wearing a dress? and is it true that we can't wear open heeled sandals/slippers as well?

From a travel site:

"When visiting temples that the utmost respect is required – usually you will be expected to wear trousers or at least knee length shorts or skirt; t-shirts with elbow length sleeves are also expected and sometimes proper shoes, i.e. not flip-flops, will be required."

It also mentions that at the Grand Palace, appropriate dress can be borrowed inside.

Yes, that is true.
You should dress nicely. Short/long pants also prohibited for women.
Skirt should be at knee level, a little shorter is still ok.
Open heeled is ok with some hieght, but sandal and slipper considered unsuitable.

If you prepare to run around practically, you can wear what you like. Before geting inside the Grand Palace, there is suitable clothes for rent. But for temples, no dress for rent. Temples are not as strict as Grand Palace, you shouldn't dress sexily or temptingly anyway. Avoid showing (part of) boobs, tummy, a*s*s, upper legs in public as Thai people view that as tempting.

Have a nice Bangkok visit

Yes, please familiarise yourself with Thai customs if you are visiting the temples. Should you forget, there are courtesy clothes for rent just outside the temple to cover yourself. There will be people at the temples to advice too if you forget.

Just something light , summer wear with long sleeve below the elbows and pants or dress length half-way below the knees.

You will need to remove your footwear before entering the temples anyway.

yeahh, it is a bit troublesome to get into there but surely you will be appreciated to go there. here it is, All Thailand information including Grand Palace... it's cool, let's try, I always recommend to all my friends. have a nice trip.

yeah because its like some kind of respect for the place i would suggest the skirt to be long covering your legs or way beyond your knees and wear closed shoes and its for men too they are not supposed to wear shorts and open men slippers