A complete compaction curve for fine-grained soil and its characteristics are discussed. The formulation of the relationship to model the curve is introduced. The equation is versatile in its ability to quantify the shape, size and position of compaction curves. It is capable of describing the compaction curve from the dry to very wet condition and can be used to predict a family of compaction curves for a given soil for different input of compaction energies. All parameters in the equation have specific physical definitions. Simple procedures to obtain all parameters directly from a standard compaction curve are developed and described in detail. The examples show that the proposed equation is good at representing the soil compaction curve and demonstrates excellent agreement between laboratory test data and the predicted curves. The family of curves predicted by the equation would improve the practice of the one-point method in the field.