How long should an undershirt be to stay tucked in?

Short answer: An undershirt stays tucked when there is enough length below the trouser waistband to stay anchored as the body moves, and when the fabric and fit do not pull it upwards. As a rule of thumb, the hem should sit well below the waistband, often several centimetres below the hip bone on the wearer, so that sitting, bending and reaching do not pull it out. Body length must allow for the wearer's torso length, the rise of the trousers (low-rise trousers need more length) and shrinkage in washing. A close, stretchy fit at the hip helps, because a loose body rides up and blouses. Extra length adds bulk only if the hem is wide or the fabric heavy, so pair a longer body with a light fabric, a slightly tapered hip and a flat hem. Many brands offer a regular and a tall or extra-long length.

What pulls an undershirt out

• Too little length below the waistband.
• Fabric shrinkage in length after washing.
• A loose body that blouses and climbs as the wearer moves.
• Sleeves or armholes that pull the body up when arms are raised.

Setting the length

• Measure body length from high point shoulder to hem.
• Compare with torso data, for example from ISO 8559 body measurement definitions.
• Allow for the rise of the trousers your customers wear.
• Add the expected length shrinkage after washing.

Fit and finish

• Taper slightly from chest to hip so the hem stays close to the body.
• Use a light jersey with some elastane for grip and recovery.
• Use a flat or bonded hem to reduce bulk at the waistband.
• Check armhole height; a low, tight armhole pulls the body up when arms lift.

Testing

Measure length before and after washing using ISO 3759 marking and ISO 5077 procedures. Then ask testers to wear samples with their own trousers, sit, bend, reach overhead and walk for a day, and record whether the shirt stays tucked.

A worked example

As an illustration, if testers report the hem pulling out when they reach up, the team might add length, taper the hip and raise the armhole slightly, then repeat the wear test after washing.

Limits

Body shapes and trouser styles vary, so no single length works for everyone. A tall option often solves more complaints than lengthening the whole range.

Facts, recommendations and uncertainty

Established: length below the waistband, shrinkage and fit decide whether an undershirt stays tucked. Recommendation: allow for rise and shrinkage, taper the hip and wear test. Uncertain: the torso lengths and trouser rises of your customers.

Sources and further reading

• ISO 8559-1:2017 — Size designation of clothes: anthropometric definitions for body measurement
• ISO 5077:2007 — Determination of dimensional change in washing and drying
• ISO 3759:2011 — Preparation, marking and measuring of fabric specimens and garments for dimensional change

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.