A measurement system, for use in RF power measurements, allows an arbitrary Bruene-type RF coupler to be calibrated at a number of different power levels and frequencies with an idealized transfer function being created for each calibration power point. Following calibration, when the coupler is used in an operational (measurement) mode, the DC voltage corresponding to the present power measurement is read, and the discrete idealized transfer functions generated during the power and frequency calibration phases are used to determine a best fit idealized transfer function, which is used in conjunction with the exact DC voltage being measured to create a highly accurate power measurement.