An undershirt can meet its flat body-length measurement and still pull out of trousers. The result depends on torso length, trouser rise, garment width, fabric recovery and the movement that lifts the hem. For an untucked design, extra length can instead create a visible tail or bunch beneath the outer shirt. Choose the wearing position first, then approve length and hem shape as a system.
Write the use conditions before adding length
The brief should identify whether the garment is always tucked, usually untucked or expected to serve both uses. Record the intended wearer height and torso range, usual trouser rise and outer-shirt length. If these vary widely, one body length may be a compromise; a separate length option needs customer evidence and its own quantity plan.
Do not interpret “stay tucked” as a universal performance guarantee. Define the movement and clothing combinations under which the sample must remain acceptable. A fit result with high-rise trousers does not automatically apply to low-rise trousers on a longer torso.
Measure front, back and the shortest side
| Measurement | Method to define | Why it matters |
|---|---|---|
| Front body length | Vertical drop from the named high shoulder datum to centre-front finished hem | Front coverage and visible tail beneath an outer layer |
| Back body length | Same defined reference convention to centre-back hem | Coverage while bending and sitting |
| Side length / side hem height | Named underarm or shoulder reference to the side-seam hem | A curved hem may have adequate centre length but inadequate side overlap |
| Hem width | Flat width at the specified position, garment relaxed | Restricted sweep or excess fabric accumulating around the waist |
| Curve or split | Drawing with fixed points and split height where present | Controls the shortest coverage point and how the hem spreads |
Keep a photograph showing each tape position. State whether the dimensions apply before washing, after washing or at both stages. A curved tape path along a side seam cannot be compared directly with a vertical body-length drop.
Choose the hem shape for the job
A straight hem offers a straightforward coverage reference but may leave more material to manage if it is long. A curved hem can allocate length to front and back while shortening the sides; that shorter side must still pass the tucked-use check. A split hem can allow movement, but the split height changes the minimum covered area and needs review under the outer garment.
Approve the hem finish as well as the outline. Check whether its seam stretches sufficiently for dressing, whether a bulky edge shows through trousers or the outer shirt, and whether it twists after washing. Confirm that the proposed curve and finish can be made consistently before treating them as approved construction.
Run a sit, stand and reach trial
- Record wearer reference, body dimensions relevant to fit, garment size, trouser rise and outer-shirt reference.
- Photograph the starting position. For a tucked trial, record front, side and back overlap below the waistband without deliberately over-stretching the garment.
- Repeat a documented sequence of sitting, standing, forward reaching and overhead reaching. Keep the sequence and repetition count the same across candidates.
- After each movement, record hem withdrawal, bunching, pressure and whether the wearer needed to adjust the garment.
- Repeat with the washed sample after the agreed drying and relaxation procedure.
Use a worksheet with columns for sample, size, care state, starting overlap, remaining overlap by location, exposed hem when untucked, bunching and adjustment required. Set the acceptable overlap or exposure limits before approval. These are brand-defined criteria for the named use case, not industry-wide length requirements.
Diagnose the result before revising the pattern
- Only the side pulls out: review side hem height and curvature before adding length to the centre front and back.
- The whole garment rises when reaching: check armhole and shoulder movement and chest tension. More length alone may hide rather than solve the cause.
- The hem bunches while sitting: review excessive length, hem width, trouser fit and fabric drag.
- The new sample passes but the washed one fails: check separate length and width changes before approving pattern compensation.
- One size fails: review the length grade and wearer proportions, then test neighboring sizes.
The existing guide to knits becoming shorter and wider after washing explains the related dimensional-change problem. For an undershirt, translate that evidence into a finished-garment movement result rather than relying on one fabric shrinkage percentage.
Lock the length decision into the size set
Give length its own grade rule instead of scaling it automatically with chest width. Retain washed measurements, the approved hem drawing and movement records at the base and extreme sizes. If changing material or neckline construction changes how the garment hangs, repeat the relevant fit checks.
Include these records with the undershirt development specification when requesting a quotation or sample through Knitwear Base. State the target fit conditions without promising that one length will remain tucked on every wearer.
