This is a gorgeous summer dress: unlike many cotton dresses of this period there is no fading or discolouration and it has been well looked after. 
SOOOO Fresh looking! And so comfortable to wear. I love such dresses for a stroll along the promenade and you want to look retro and feminine but don't want to be too restricted. I ran along the beach without shoes in it afterwards! So many compliments as it is that fresh looking. It billows and clings in the wind, but doesn't blow right up so its decent to wear without petticoats!
The fabric print is in a crisp white background with lilac, green and sky blue pastel colours. Divinely pretty!
But I am going to include the lilac coloured gloves in this purchase as they go with the dress so well and it would have been almost unthinkable not to wear gloves back when this was made; especially if you are going for a cream tea after your walk along the beach!

No label so possibly hand made, and unlined, but at some point it has been taken up 3 1/4 inches; so it could feasibly be let down again. 
I imagine being likely an early 60s or late 50s dress, it was taken to knee length as hemlines rose. 
The waist is gathered and the skirt isn't a full circle but you could wear a petticoat with it. The waist is set quite high so I am 5ft 5 ins & it's just about fine for me, but would suit anyone more petite in height ideally. Many such dresses drown the smaller height so this is perfect. 
Size wise it has a 30" waist & 35" bust; hips obviously free as it flares out. So I'd say a 10 to a small 12 UK but an 8-10 could get away with it.
39 inch length though you have that extra 3 and a quarter inches that could be let down if you aren't so petite and want a 50s length. 
I bought it as a cotton blend but looking at it if it is blend at all it is a slub silk.