Thread conversion chart, by measured colour distance
Give a brand and a code and get the nearest thread in every other brand we hold, each with the ΔE2000 distance between them. No conversion is exact, and this page says how far from exact each one is.
DMC, Anchor, Madeira and other names are trade marks of their owners. We are not affiliated with them and do not reproduce their conversion tables: matches are computed here. How we use brand names
How the distance is measured, and what it cannot tell you
Every thread we hold is stored as an sRGB value and converted once into CIELAB against the D65 white point. CIELAB is a space built so that a given step in it looks like roughly the same size of colour change wherever you take it, which sRGB is not: the numeric difference between two RGB triples has almost nothing to do with how different the colours look.
Distances are then computed with CIEDE2000 — ΔE2000 — the current CIE recommendation, which corrects CIELAB for the places where it still misjudges: it weights lightness, chroma and hue separately and carries a correction term for the blue region, where plain CIELAB distances are notoriously too large. Roughly, ΔE2000 near 1 is the threshold at which a trained eye can see a difference at all under good light.
The nearest few colours in each brand are computed for every colour in advance and stored, so this page reads a table rather than doing colour science while you wait. The same table is what the pattern editor and the shopping list read, so the answer here cannot disagree with the answer elsewhere on the site.
Where the sRGB values come from matters, so it is recorded per colour: manufacturers publish digital values for some ranges, and where they do not, values are derived from published sources and marked as such. A colour whose provenance is a derivation is not less carefully handled, but it is one step further from the physical thread than one the manufacturer published.
And the part every printed conversion chart leaves out. A substitution is never exact, and the number on this page measures only one of the reasons. Dye lots differ within a single brand. Mercerised cotton, matte cotton, silk and wool return light differently, so two threads that measure the same can read differently in the finished piece. The cloth beneath shows through and shifts what sits on it. Above all, two colours that match under one light can separate under another — metamerism — which is why a match judged under a shop's lamps can be wrong at your table.
So: treat a distance under 2.0 as safe, one under 3.5 as a substitution worth making deliberately, and anything beyond as a different colour that happens to be the closest we hold. When the shade is what the design is about, buy one skein and stitch a corner before you buy the rest.