Because you cannot bend metal at an exact 90 degrees, calculating the distance between two bends and two subsequent legs of a bend requires a mathematical formula and knowing the bend radius, material composition, hardness, and material thickness. These formulas are a bit outside the scope of this article, but should be something you learn more about if you get into making multiple parts or you make something a person’s life depends on. Our plan is to bend sheetmetal for noncritical parts like interior or roof panels. To get measurements, we will make a sample bend and use it to determine outside dimensions. If you care, look up bend allowance, K-factor, and setback. That ought to keep you busy for a while.