The actress' original script from the film was also among the items at the sale in Beverly Hills, California, which in total raised $2.4m.
Some of the proceeds will go towards Newton-John's cancer treatment centre in Australia.
The buyers' identities are not public.
Grease was released in 1978 and Olivia Newton-John played demure Sandy alongside John Travolta as bad boy Danny.
The infamous black outfit marked Sandy's transition from a good girl high-schooler to a sexy, leather-clad biker chick, when the couple sang You're the One That I Want in a fairground.
The leather trousers were already two decades old when she wore them and had a broken zip that meant Newton-John had to be sewn into them.
She said that "limited" what she could eat and drink while filming, adding "those were long days".
The pink gown she wore to the film's premiere sold for $18,750, Julien's Auctions confirmed - three times the estimate.
Newton-John has asked buyers to send her photos of themselves with the items along with a personal note.
She said selling a large amount of her possessions was a "simplification of my life".
Aged 71, the British born Australian actor is currently undergoing treatment for stage four breast cancer.