Darts and princess seams do the same job: they take flat fabric and give it the curve of a bust, a waist or a hip. A dart does it in one stitched fold that tapers to a point, which is quick to sew, leaves the surface of the fabric uninterrupted and suits crisp fabrics and prints. A princess seam spreads the same shaping along a curved seam from the shoulder or armhole down through the bust, which fits a fuller or more varied figure more smoothly and is easier to adjust by small amounts, at the price of more pieces, curved seams and lines across any print. Choose darts for a shift dress, a blouse or a first fitted project; choose princess seams for a closely fitted bodice, a bust far from the standard draft, or a jacket.
How do darts and princess seams compare?
| Feature | Darts | Princess seams |
|---|---|---|
| What it is | A fold stitched into a tapering point | A shaped seam joining two panels |
| Where the shaping sits | Concentrated at the dart point | Spread along the whole seam |
| Pieces to cut | Fewer (one front, one back) | More (center and side panels) |
| Sewing skill | Easy; pressing the point well is the craft | Moderate; curves, clipping, easing |
| Fitting | Move, shorten or deepen the dart; an FBA splits it | Pinch or let out anywhere along the seam |
| Fabrics | Crisp, stable fabrics; large prints | Most fabrics; stripes and plaids need matching |
| Look | Clean surface; the point can show | Vertical lines that lengthen the figure |
| Typical garments | Shift dress, blouse, pencil skirt, trousers | Fitted bodices, bustiers, jackets, coats |
What does a dart actually do?
Lay a rectangle of fabric over a bust and it stands away at the sides. A dart removes that excess: you fold a wedge out of the fabric and stitch along it, from the wide end at the seam to nothing at the point, which lands a little short of the bust point. The fabric inside the fold is gone from the outline and the piece now cups.
Darts come in from the side seam (a bust dart), up from the waist (a waist dart) or both, and the same principle shapes a skirt or trousers over the hip and seat. A dart's intake, the width of the wedge, is set by the difference between two measurements: bust to underbust, or waist to hip. The larger the difference, the wider the dart, which is why one dart can only do so much before it puckers at the point. How to sew darts covers the stitching and the pressing that makes the point disappear.
How does a princess seam shape a bodice?
A princess seam takes the same wedge and spreads it along a seam. Rather than folding the excess out of one piece, the pattern is split into a center panel and a side panel, and the two edges that meet are drawn as different curves: convex on one, concave on the other, with the biggest difference at the bust. Sewing those two curves together builds the same shape as a dart, but the shaping is spread over 20 cm (8 in) or more instead of focused on a point.
The seam can start at the shoulder (the classic princess line) or at the armhole (an armhole princess seam, which gives a slightly softer curve over the bust). Both continue down through the waist, so one seam shapes bust, waist and hip in a single line, and on a dress the panels can flare out toward the hem.
Which is easier to sew?
Darts, in most cases. A bust dart is one straight or slightly curved line, stitched from the seam edge to the point and pressed over a tailor's ham to set the curve. The one skill is finishing the point without a pucker: shorten the stitch for the last centimeter (3/8 in), run off the edge of the fold, and tie the threads by hand instead of backstitching.
A princess seam asks more. The two curved edges are different shapes, so the convex side panel is eased onto the concave center panel: pins every 2 cm (3/4 in) around the bust, stitching with the fuller layer underneath so the feed dogs ease it in. After stitching, the seam allowance needs clipping and notching so it lies flat around the curve, then careful pressing over the ham. It takes about twice the sewing time of two darts, though the result rewards it: a smooth curve with no point to pucker.
Which is easier to fit and alter?
Here princess seams win. Fitting happens along a seam that runs the full length of the bodice, so you can pin out a little at the waist, let out at the bust and take in at the hip, each in its own place, on a toile or even on the garment itself. Increasing the cup size means adding width and length to the panels around the bust, which is a smoother change than splitting a dart.
Darts can be moved, lengthened, shortened and made deeper, and most fit adjustments were invented for them: a full bust adjustment slashes the bodice through the dart to add room, and shortening a dart fixes a point that pokes. But a single dart with a large intake, say more than 5 cm (2 in) at the seam, pulls the fabric into a cone that no pressing fully hides. Beyond that point two darts, or a princess seam, carry the shaping better.
Which fabrics suit darts, and which suit princess seams?
A dart leaves the fabric's surface whole, so large prints, border prints and anything you want to show uninterrupted favor darts. Crisp fabrics such as cotton poplin, linen and gabardine press into a sharp dart that holds. Sheer fabrics show the dart's fold from outside, which some people dislike; it can be made a feature with a French dart, one long diagonal dart from the side seam toward the bust.
Princess seams suit soft and medium fabrics that ease around a curve: wool crepe, cotton sateen, ponte, silk twill. Stripes and plaids need thought, because the vertical seam shows any mismatch and the curve means the motif cannot match the whole way down. Stiff fabrics resist the ease at the bust and pucker, and very thick fabrics make bulky seam allowances around the curve.
Can you turn darts into princess seams?
Yes, and that is how most princess patterns are drafted. The bust dart is rotated on paper so that it points toward the shoulder or the armhole, then it is extended down through the waist dart, and the pattern is cut along that line into two panels. The dart's intake becomes the gap between the two curved edges. Drafters call this dart manipulation, and it works in reverse too: close the princess seam at the bust and the excess reappears as a dart.
Which means the choice is a style and construction decision, not a fit limit. A made-to-measure draft already sizes the dart intake to your own bust-to-underbust difference: Sewly's shift dress and fit-and-flare dress, for instance, are drafted from flat-pattern blocks with your measurements, so the darts match your shape rather than a standard size's.
Which should you choose?
- A first fitted project, or a project you want finished this weekend: darts. Fewer pieces, straighter seams, a quicker press.
- A loose or semi-fitted shape such as a shift, a boxy blouse or an A-line dress: darts, or a small bust dart alone. The shaping is modest and the ease does the rest.
- A closely fitted bodice, a strapless or sleeveless style that must hug the body, or a jacket: princess seams. The shaping is continuous and the fit can be tuned along the seam.
- A bust more than two cup sizes larger or smaller than your pattern's draft: princess seams, or two darts (side and waist) that share the intake.
- A large print, a border print or a sheer: darts, placed to keep the motif whole.
- Stripes or plaids: darts unless you enjoy matching, and then a princess seam with the stripe running straight on the center panel.
Both answer the same question: where does the excess go? Pick the one that sews and fits best for this fabric and this body, and remember that a toile in cheap cotton will tell you in an hour.