How deep should an undershirt V-neck be?

Short answer: The aim is a V-neck that stays hidden under an open-collar dress shirt with one or two buttons undone, while still looking acceptable on its own. A deeper V hides better under open collars but can look exaggerated and may need more support to stop it stretching. Measure the V depth from the high point shoulder or centre back neck to the point of the V and compare with where shirt buttons sit on typical customers. Many brands offer a standard and a deep V. Grade the depth with size so larger sizes keep the same proportion, stabilise the V with a well-sewn binding or rib and tape, and test with real shirts on testers.

How to choose depth

• Compare V point with the second shirt button on testers.
• Consider offering standard and deep V options.
• Check appearance when worn alone.

Measuring

• Measure from high point shoulder or centre back neck to V point.
• Grade with size.
• Use body measurement data such as ISO 8559 for neck and chest ranges.

Stability

• Use binding or rib with correct tension.
• Stabilise the V point with a neat mitre or overlap.
• Wash test with ISO 6330 to check stretching.

A worked example

The brand fits its undershirt with dress shirts on testers with one and two buttons open. The current V shows with two buttons open. It adds a deep V option about 3 cm deeper, graded by size, and keeps the standard V for customers who wear ties.

Undershirt fabric choices

Undershirts are worn next to the skin under a shirt, so a light, smooth fabric such as fine cotton, modal or a moisture-wicking blend helps the V lie flat and avoids showing lines through a thin dress shirt. Light colours close to skin tone are often less visible than bright white under light shirts.

Neckline finish

A narrow binding usually lies flatter than a wide rib and is less likely to show at the open collar. Check the finish does not curl after washing, since a curled edge shows through and looks untidy.

Limits

Shirt styles and body shapes vary, so no single depth suits everyone.

Facts, recommendations and uncertainty

Established: V depth determines whether an undershirt shows under open collars. Recommendation: test with real shirts and offer standard and deep options. Uncertain: which depth your customers prefer.

Sources and further reading

• ISO 8559-1:2017 — Size designation of clothes: anthropometric definitions for body measurement
• ISO 6330:2021 — Domestic washing and drying procedures for textile testing

Standards and regulations are referenced by their published scope. Test parameters, cycles and pass levels should be agreed with your laboratory for the specific product; legal requirements should be confirmed for each destination market.