The purl problem

Stockinette knit flat alternates knit rows and purl rows; stockinette in the round is knit stitches only. Most knitters purl at a slightly different tension than they knit — commonly a bit looser. Flat stockinette averages the two tensions; circular stockinette is pure knit tension.

The gap (sometimes called "rowing out" when visible as uneven stripes on flat fabric) typically amounts to half a stitch to a full stitch per 4 inches, and can be more. One stitch per 4 inches on a 44-inch sweater is over two inches of circumference — a full size.

How to swatch for a project knit in the round

The honest method is to swatch in the round, and there's a shortcut that avoids knitting a full tube:

1. Cast on onto a circular needle or two double-points, enough stitches for at least 6 inches of width.
2. Knit one row. At the end, do not turn. Slide the stitches back to the right-hand tip, carrying the working yarn loosely — very loosely — across the back.
3. Knit the next row from the same side again. Every row is a knit row, exactly like working in the round.
4. Continue until the swatch is at least 6 inches tall, then cut the loose back strands so the swatch lies flat, wash, block, and measure the center.

Already mid-project and the gauge shifted?

Measure your actual gauge directly on the live project — lay it flat, unstretched, and count stitches per 4 inches away from the needles, ideally after gently wetting and drying a section if you can. Then compare with the pattern gauge and decide:

• Small difference (≈ quarter stitch per 4 inches): blocking will probably absorb it; continue.
• Half a stitch or more: recalculate the remaining instructions at your real gauge with the gauge calculator — the method in adjusting a pattern for a different gauge works mid-project too.
• A full stitch or more on a fitted garment: seriously consider restarting at the correct needle size; two inches of unplanned ease rarely blocks away.

Other reasons round gauge drifts

• Needle change: switching between the circular needle used flat and double-points or magic loop changes tension for many knitters.
• Ladder zones: loose columns at needle joins on DPNs or magic loop can add width without changing true gauge — measure away from the joins.
• Relaxation over time: early rounds knit tight from cast-on nerves loosen as you settle in. Measure gauge after a few inches, not on round 5.
• Colorwork: stranded sections almost always knit tighter than plain stockinette — swatch colorwork separately, in the round.

The takeaway

If the project is knit in the round, swatch in the round — and measure the blocked swatch properly. If your circular gauge still doesn't match the pattern, that's a normal, fixable situation: here are your options.