The solid geometry questions on the ACT will always ask you about volume, surface area, or the distance between points on the figure. The way they make it tricky is by making you compare the elements of different figures or by making you take multiple steps per problem.
Every solid geometry question on the ACT is concerned with either the volume or surface area of a figure, or the distance between two points on a figure. Sometimes you'll have to combine surface area and volume, sometimes you'll have to compare two solids to one another, but ultimately all solid geometry questions boil down to these concepts.
No matter the format, each type of ACT solid geometry question exists to test your understanding of the volume and/or surface area of a figure. You will be asked how to find the volume or surface area of a figure or you'll be asked to identify how a shape's dimensions shift and change.
Before we go through the formulas you'll need to tackle solid geometry, it's important to familiarize yourself with the kinds of questions the ACT will ask you about solids. ACT solid geometry questions will appear in two formats: questions in which you are given a diagram, and word problem questions.