There are two ways of introducing appropriately sized darts.
Method #1 : Two waist darts are added before the "basic bra block" is drawn in. The width of the basic waist darts are determined by the difference in measurement between the bust measurement and the waist measurement, divided by two (because the basic block is only half the garment), and then divided by three (there are three waist darts, the two shown and one in the middle that is lost in the overlapped region). Bust – Waist ----------------2
/ 3 = Width of Waist Dart
Bust - Waist 6 = Width of Waist Dart
For the purposes of the bra construction, the width of both the waist darts and the front bodice dart are doubled, so as to create a raised "cup" shape for the breast.
Method #2 : A somewhat more accurate way of estimating the dart sizes is by using an "overbust" and an "underbust" measurement, in addition to the bust measurement itself. The width of the dart along the top line of the bra form is determined by half the difference between the overbust and the bust, Bust – Overbust = Width of the dart along the top line 2
The width of the front dart along the bottom of the bra form is half the difference between the bust and the underbust measurement, minus the small dart width associated with the back dart (width about 2.5 cm or 1" at the waist level). Bust – Underbust = Width of the front dart along the bottom 2
Shown also are the side seam located at the central line (B-G), and the "forward front seam" which is to the right of the side seam and tilted forward at the bottom. The upper edge of the basic bra block is constructed by * Marking the left edge at Centre Back (CB) 1.5 cm above the bust line (point A); * Marking the central seam 2.5 cm above the bust line (point B); * Marking each side of the bust dart a distance of 9.0 cm from the bust point (points C and D - note that the lines shown follow the doubled dart size, not the dart shown); * And marking the rightmost edge 2.5 cm above the bustline (at Centre Front CF, point E). * The points A-B-C-D-E are then connected by lines. For small sizes, reduce each of these measurements by 0.3cm, while for plus sizes, add 0.5 cm to each measurement. The lower edge of the basic bra block is constructed by * Marking the leftmost edge (point F) 2 cm below the bustline; * Marking the side seam (point G) 4.5 cm below the bustline; * Marking the two sides of the front waist dart (points H and I) at a distance of 7.5 cm from the bustpoint (BP); * And marking the rightmost edge 2.5 cm below the bustline (point J at CF). * The points F-G-H-I-J are then connected by straight lines. As for the upper edge, the distances are reduced by 0.3 cm for small sizes and increased by 0.5 cm for plus sizes.