Fill density: why 0.25 mm between rows is the standard

Fill density is the gap between the rows of a fill stitch. Some software and stitch guides talk about values around 0.4 mm, others default to 0.25 mm, and both can describe the same coverage on fabric. Mixing the two up is one of the easiest ways to end up with a thin, see-through fill.

Two ways to measure the same rows

Some programs measure from one row to the next row running in the same direction, so the number spans two passes of the needle. Others measure between adjacent rows. A setting of about 0.4 mm in the first convention lands close to 0.2–0.25 mm in the second.

What happened on our first files

Our first Fox Scout and Fiery Wolf files used 0.40 mm between adjacent rows: a two-row number typed into an adjacent-row setting. On screen they looked fine, but their fills had far fewer rows than standard. We caught it while building our next design and re-issued both files at 0.25 mm adjacent spacing.

How to check a file you bought

• Zoom in on a large fill in your machine software and count the rows across 1 cm. About 40 rows per centimetre matches 0.25 mm adjacent spacing.
• On a test sew-out, hold the fabric up to a light. A healthy fill doesn't show pinholes of fabric between the rows.
• Light thread on dark fabric needs a little more coverage than dark thread on light fabric. We go slightly tighter (about 0.23 mm) for light threads.

When to go lighter

Very stretchy knits, small areas under about 5 mm and details that sit on top of another fill can all run lighter. That's a decision per object, not one global number, which is why we set density object by object.