Tank top design.

The three numbers that define it

A tank top pattern is defined by three measurements before anything else, and the rest of the garment follows from them.

Strap width. At the shoulder, finished. Two centimetres reads as athletic, four to five as a relaxed vest, one or less as a camisole. It's the single most defining measurement on the garment.

Armhole depth. From the shoulder point straight down to the bottom of the armhole curve. Deep armholes read as relaxed and expose more of the side of the body; shallow ones read as fitted. This is also where a tank goes wrong most often, because a deep armhole on a wide body means the side of the garment gapes open when the wearer moves.

Front neck drop. Independent of the armhole, and the one people adjust last when they should adjust it first. It sets whether the garment reads as a vest or as something more open.

Finishing a curved edge in jersey

Here's the actual problem. Single jersey curls, and a curved cut edge curls unevenly, so a tank armhole cannot simply be hemmed the way a straight t-shirt hem can. Three approaches:

• Self-fabric binding. A strip of the body fabric, cut across the stretch, folded over the edge and attached with a binder attachment. Clean, flexible, industry-standard for knit tanks. The strip is cut shorter than the edge and stretched on — the same ratio logic as a neck band, and it's the number people leave off.
• Rib binding. Same construction with rib instead of self-fabric. More recovery, more visible, and a second fabric row in the bill of materials.
• Turned and cover-stitched. Possible on a shallow curve, difficult on a deep one, and it will ripple if the curve is tight. Cheapest, and the one that looks cheap.

Whichever you pick, the binding width is a spec value and the stretch ratio is another. A binding attached at 100 % of the armhole length gapes; at 85 % it lies flat.

Where the straps meet the body

Two constructions, and they change the garment. Cut-on straps mean the strap is part of the front and back panels, joined at a shoulder seam — simple, stable, and the strap width is fixed by the pattern. Separate straps mean a strip attached at both ends, which allows a narrower strap than a cut-on pattern comfortably supports, and adds two attachment points that need reinforcing.

Fabric

140 to 200 g/m² single jersey covers most tanks. Elastane matters more here than on a t-shirt: a tank has less fabric holding it in shape, so a jersey without recovery grows at the straps and the armholes visibly. Two to five per cent is worth the cost on anything fitted.

For a ribbed tank, the whole garment is rib and the pattern is cut with negative ease — narrower than the body — with the fabric doing the fitting. That only works with good recovery, so elastane stops being optional.

Points of measure

Nine to twelve, which makes it the shortest tech pack on the site. Chest, sweep, body length front and back, shoulder to shoulder at the strap, strap width, armhole depth, armhole opening, front and back neck drop, and the binding width. Note that a bound edge carries its allowance in the binding, not in the panel.

Jersey weights and curl · the t-shirt it comes from · allowances on bound edges · the garment catalogue