A swatch that tells you more than the needle label

Give the middle somewhere to settle

Begin with a piece noticeably wider than the area you intend to measure. A border can keep the edges orderly, but it can also pull the centre into a shape that the full garment will never have. Leave several stitches between that border and the measured area. For a textured pattern, include complete repeats rather than stopping halfway through a cable or rib.

Keep the sample in the same kind of knitting as the project. A flat sample and fabric worked in the round may differ because the hands treat knit and purl rows differently. The aim is not to make a laboratory specimen. It is to reproduce the ordinary rhythm you will use on the sofa, including the pauses that happen when the kettle needs attention.

• Use the intended stitch pattern.
• Allow a generous margin around the measured area.
• Record the needle size and material.

Measure before doing anything clever

Take the work off the needles without stretching it across a tight cast-off edge. Lay it flat and let it rest. A ruler placed over the middle is easier to read than a flexible tape pulled between two fingers. Count complete stitches and the fractions at each end; rounding both ends away can make a small sample look more regular than it really is.

Record width and height, but also describe the handle. Does it spring back after a light squeeze? Does the reverse feel pleasant against the wrist? Can the fabric support its own weight without becoming stiff? A note such as soft but rather open is often more useful later than another decimal place in a gauge calculation.

Treat it as the garment will be treated

Use the care method intended for the finished piece and follow the yarn's care guidance. Press out excess water gently and support the sample as you move it. Lay it on a towel without forcing it to reach a preferred number. A square stretched to match a pattern measurement tells you mostly how effectively you can stretch a wet square.

Let it dry fully before measuring again. The surface can feel dry while the thicker areas still hold moisture. In a small London flat, the safest place is often an ordinary table out of the way, rather than a hot radiator. The important comparison is between two settled states, not a dry first measurement and an impatient second one.

Keep the decision with the evidence

Attach a loose label with the stitch count, row count, needle and washing method. If you try another needle, keep both samples. Put them beside each other before deciding which fabric suits the project. One may match the written gauge while the other makes a far better scarf; those are different questions and deserve separate answers.

The final note should say what you will change. It might be a different size calculation, a firmer cuff or a decision to use the yarn for something smaller. Store the sample where it can be found again. A row of labelled squares is a modest reference library, and unlike a remembered impression it remains available when the project is picked up after winter.