The objective of this work was the development of a real-time capable in-cylinder pressure based diesel engine-out PM estimator. Two types of experimental passenger car DI diesel engines, equipped with in-cylinder pressure sensors have been used for the PM estimator development. Measurements have been taken during steady state and transient operation on an engine test bench. Using the Engine ECU signals and in-cylinder pressure data new parameters have been derived and used as inputs for an exponential zero dimensional modeling approach. Good correlation between the estimated and measured PM has been achieved for various experiments, not only for steady state operation points but also for transient measurements. Particularly, the model delivers good qualitative results, as well as good quantitative results in some regions. PM gradients, that is, the tendency of PM to increase or decrease from one engine operating point to another are represented successfully. Considering that the PM estimator is intended to be used with a model based engine controller, for increasing or decreasing PM emissions when necessary, the accuracy of the model is more than sufficient. Moreover using this simple exponential approach requiring little computational effort, the engine ECU is capable of cylinder-specific PM emissions calculation, significantly faster than in real-time. The estimator has also been implemented on an experimental vehicle with a bypass engine ECU and will provide new possibilities in the field of combustion control in the future. © 2011 SAE International.