How does forever21.com determine shipping cost?

Few days ago i ordered a a clutch and 2 headbands shipping was $5.95 and today i was going to order a dress and hat and it said shipping was $6.95...How is shipping cost determined?How does forever21.com determine shipping cost?yeppp usually by weight and/or price nor size? idk :) but i think weightHow does forever21.com determine shipping cost?usually by weight