Makers often create both physical and digital prototypes to explore a design, taking advantage of the subtle feel of physical materials and the precision and power of digital models. We introduce ShapeMe, a novel smart material that captures its own geometry as it is physically cut by an artist or designer. ShapeMe includes a software toolkit that lets its users generate customized, embeddable sensors that can accommodate various object shapes. As the designer works on a physical prototype, the toolkit streams the artist's physical changes to its digital counterpart in a 3D CAD environment. We use a rapid, inexpensive and simple-to-manufacture inkjet printing technique to create embedded sensors. We successfully created a linear predictive model of the sensors' lengths, and our empirical tests of ShapeMe show an average accuracy of 2 to 3 mm. We present an application scenario for modeling multi-object constructions, such as architectural models, and 3D models consisting of multiple layers stacked one on top of each other. ShapeMe demonstrates a novel technique for integrating digital and physical modeling, and suggests new possibilities for creating shape-aware materials.