As the first step in building a model, set the scale to match the size of the real objects they photographed in order to estimate their true surface area and volume. Once set, the approximation is as good as the model that is created. Use just one or two shapes for a quick estimate. Use more shapes to add detail and to get a closer approximation.

Building with 3D shapes on top of a 2D image is a great way to notice what dimensions are at play and to get a sense of where the formulas come from.

This is particularly useful for Lessons such as Which is Greatest? and Make a Model.