Piezoelectric, drop-on-demand ink jets typically require a long development cycle and numerous redesigns to meet design goals. Numerical modeling of the ink jet can be used to speed this process and improve the overall result of the development effort. By using a combination of modeling tools such as finite-element structural and fluid modeling and a proprietary lumped-parameter model of the ink jet, ink jet performance can be estimated without the need to fabricate and test. This can save significant develop time and effort. Investigations of ink jet dimensions such as PZT thickness, pumping chamber, nozzle and other dimensions, and their effect on performance characteristics such as drop mass and velocity, input voltage and frequency response help guide the design of prototype ink jets. Sensitivities to fabrication tolerances can be minimized by determining performance optimums and selecting design points with low sensitivities to known tolerances. Spectra Inc. has applied these tools to the development of high frequency, high performance ink jet designs. Ink jet performance data and comparison to model predictions help improve the modeling tools.