QuickField uses the empirical Bertotti formula for the core loss calculation:
p = khf B2 + kcf2B2 + ke(f B)1.5
Here B - magnitude of the module of the flux density vector per period, f - problem frequency, kh, kc, ke - volume power loss coefficients for specific magnetic material.
Usually magnetic material vendors supply each material with the curves or tables of the core loss density vs. flux density on various frequencies. It is possible to approximate these experimental data by Bertotti formula by adjusting the loss coefficients. This process is called "curve fitting".
Off-line version of Core loss coefficients calculator (Microsoft Excel spreadsheet) is used to automate calculation the core loss coefficients on given dataset.
See example laminated core iron loss.