Enter the total weight of the flour in your dough to find out whether challah must be separated, and whether a bracha is recited.
Shiurim used (standard/common opinions): a bracha is recited from about 3 lb 11 oz (approx. 1.666 kg / 1666 g) of flour; challah is separated without a bracha from about 2 lb 11 oz (approx. 1.230 kg / 1230 g). Below that no challah is separated. Consult your Rav for practical questions.