Dart Manipulation Calculator

This calculator splits a single bust dart's total shaping angle across multiple new darts, a core technique in dart manipulation for fitting garments to the body. Enter the Total Bust Dart Angle from your base pattern or sloper and the Number of Darts you want to distribute it across, and the calculator divides the angle evenly to give Angle per Dart. From there it derives Width per Dart and Dart Depth using standard triangle geometry: each dart is treated as an isosceles triangle with two legs equal to Bust Radius, so the dart's width at the seamline is 2 x radius x sin(angle / 2), and its depth is radius x (1 - cos(angle / 2)).

Total Bust Dart Angle and Number of Darts both move Angle per Dart by comparable magnitude, just in opposite directions -- doubling the dart count roughly halves the angle each one needs to carry, while doubling the total angle doubles it. Bust Radius and Dart Pickup per Dart, by contrast, are genuinely inert to Angle per Dart: the angle split depends only on the total angle and how many darts share it, not on the garment's size or how much fabric each dart gathers at the seam. This tool assumes the total angle is split evenly across all new darts; real patternmaking often distributes shaping unevenly between darts (for example, a princess seam versus a waist dart), a design choice this calculator leaves entirely to the patternmaker.