A medium sized Bern Watts bicycle helmet weighs 550 grams or 19.4 ounces.
I bought mine from Bobbin Bicycles, the best bike shop in London for accessories.
Stylish bicycle helmets are hard to come by, especially for ladies. Big bike shops seem to think that men only want helmets with lightening bolts or flashy stripes, and that women only want to wear pink. Finding the awesome selection at Bobbin came as a relief.