Core losses {generally iron losses or no-load losses} are not so much calculated, but measured with a 3ø power analyzer in terms of watts and vars. They are highly reactive, so are of very low [lagging] power factor.
If part of the specs and purchase order, they are published in a certified test report along with load losses.
Scott35, maybe you can comment on the legal aspects of [drytype] transformer losses in California? ;`\
