Yarn Substitution Calculator

Free yarn substitution calculator: verify any substitute yarn — by weight class, gauge, or wraps per inch — with a traffic-light verdict, hook and needle sizes, and the exact yards and skeins to buy.

Quick answer

To substitute yarn safely, match the weight class (or gauge within ±1 stitch per 4 inches), then buy by total yardage, never skein count — pattern skeins × yards per skein, plus a 10–15% margin. Enter both yarns by weight class, measured gauge, or wraps per inch and this calculator returns a traffic-light verdict, the hook and needle range, and the exact skeins to buy.

Pattern yarn

Describe it by

Yarn weight class

Skeins called for

Yards per skein

Substitute yarn

Describe it by

Yarn weight class

Yards per skein

Grams per skein (optional)

Fine-tune (optional)

Pattern fiber

Substitute fiber

Project

Workable with adjustments

#3 Light is 1 class lighter than the pattern's #4 Medium.

skeins to buy

1,150

yards (+15%)

4.5–5.5 mm (US 7–I-9)

hook for #3 Light

3.75–4.5 mm (US 5–7)

needle for #3 Light

Pattern total: 1,000 yd · 1,052 m with margin

Always crochet or knit a gauge swatch with the substitute and block it before buying the full amount — this verdict is an estimate, not a guarantee.

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How to substitute a different yarn in a pattern

Work out how many skeins of your yarn replace the yarn the pattern asked for — before you buy, not after.

Describe the pattern's yarn
Enter what the pattern calls for: the weight class, or the gauge, or wraps per inch — whichever the pattern actually tells you. Patterns are inconsistent about which they publish, so any of the three is enough to start.
Enter the pattern's skein count and length
Type how many skeins the pattern calls for and how many yards are in one. Total yardage is what really matters, and it is the number patterns bury in the small print.
Describe your substitute yarn
Enter the yards per skein and the grams from the label of the yarn you actually want to use. Two yarns in the same weight class can differ by a third in yardage per skein, which is exactly how people run out.
Read how many skeins to buy
You get the number of skeins of your yarn that match the pattern's total yardage. Round up and buy the spare in the same trip, while the dye lot still matches.
Swatch both yarns, then enter the measured gauges
Switch both yarns to Gauge mode and type what each blocked swatch actually measures — that alone can turn a red verdict green. That is what makes the verdict mean something: two measured gauges are allowed to decide the traffic light, and nothing else is. Describe a yarn by its weight class or by wraps per inch and the calculator knows only its class — it fills the gauge in from that class's midpoint, an average it refuses to let rule on your swap, so a half-measured comparison falls back to how far apart the two classes are. What measuring does not move is the shopping list. The skeins to buy come from the pattern's stated total plus the safety margin, and gauge enters neither; the one way measuring changes the count is by landing a yarn in a different weight class, which shifts the margin between 10% and 15%.

Brand Databases Find Yarns — This Calculator Verifies Them

Substitution databases match one branded yarn to another from a catalog. That works until your yarn has no catalog entry: handspun, indie-dyed, discontinued, or the unlabeled ball at the bottom of the stash. This tool checks the swap itself — any yarn against any pattern — using the Craft Yarn Council standard that every label already follows. Describe both yarns by weight class, a measured gauge swatch, or wraps per inch, and the verdict tells you whether the fabric will behave. Already know the yarn and just need quantities for a blanket? The crochet yarn calculator prices a project from scratch.

CYC yarn weight classes — gauge, hooks, needles, WPI

Weight class	Knit sts/4″	Crochet sc/4″	Needle	Hook	WPI	~yd/100g
#0 Lace (Cobweb, thread, 2-ply)	33–40	32–42	1.5–2.25 mm (US 000–1)	1.6–2.25 mm (US steel 6–B-1)	19–35	600–1000
#1 Super fine (Sock, fingering, baby, 4-ply)	27–32	21–32	2.25–3.25 mm (US 1–3)	2.25–3.5 mm (US B-1–E-4)	14–18	350–450
#2 Fine (Sport, baby)	23–26	16–20	3.25–3.75 mm (US 3–5)	3.5–4.5 mm (US E-4–7)	12–14	300–350
#3 Light (DK, light worsted)	21–24	12–17	3.75–4.5 mm (US 5–7)	4.5–5.5 mm (US 7–I-9)	11–12	230–290
#4 Medium (Worsted, afghan, aran)	16–20	11–14	4.5–5.5 mm (US 7–9)	5.5–6.5 mm (US I-9–K-10.5)	9–11	190–220
#5 Bulky (Chunky, craft, rug)	12–15	8–11	5.5–8 mm (US 9–11)	6.5–9 mm (US K-10.5–M-13)	7–9	100–140
#6 Super bulky (Super chunky, roving)	7–11	6–9	8–12.75 mm (US 11–17)	9–15 mm (US M-13–Q)	5–6	60–90
#7 Jumbo (Jumbo, arm-knitting roving)	1–6	1–5	12.75–25 mm (US 17+)	15–25 mm (US Q+)	1–4	30–50

The calculator's own canon table — Craft Yarn Council standard classes with community-standard WPI and yardage ranges. Real labels vary ±10%.

Substitute by Yardage, Never by Skein Count

The most expensive substitution mistake is buying the pattern “8 skeins” in a different yarn. Skeins are not a unit: a pattern calling for 8 skeins of a 200-yard worsted needs 1,600 yards of fabric. Substitute a 280-yard DK skein and the buy list becomes 7 skeins (15% margin included) — not 8. The calculator always converts through total yardage, and if you enter grams per skein it prices the buy in grams too. Planning a whole blanket instead? The granny square blanket calculator works out squares and yardage from bed sizes.

No Label? Count Wraps Per Inch

Wrap the mystery yarn snugly around a ruler — strands touching, not squashed — for exactly one inch and count the wraps. Nine to eleven wraps is a worsted; fourteen to eighteen a fingering. The WPI mode maps the count to a weight class using the table above, which is precisely what a brand database cannot do for a yarn that is not in its catalog. It is a ±1–2 wrap art, so treat the class as a starting point and let a gauge swatch settle it.

Fiber Changes the Fabric

Two yarns at identical gauge can behave completely differently. Wool stretches and recovers — patterns silently assume it. Cotton has no memory: ribbing relaxes and fabric grows. Acrylic refuses blocking, so what comes off the hook is final. Silk, bamboo, and alpaca drape heavily and lengthen fitted pieces. The fine-tune panel folds these behaviors into the verdict, and warns hardest when you are substituting into a fitted garment. Choosing colors as well as fibers? The granny square pattern generator previews whole-blanket combinations before you buy. Whatever the verdict says: crochet a swatch, block it, and measure — ten minutes of swatching beats re-buying a project.

Frequently Asked Questions

Is there a website that tells you what yarn to substitute?

Brand databases like YarnSub suggest named alternatives for a specific branded yarn. This calculator does the other half of the job: it verifies whether ANY yarn — including handspun, indie-dyed, or a stash ball with no label — is a safe swap, by comparing weight class, gauge, or wraps per inch and computing the exact yardage to buy.

How do I substitute yarn by yardage instead of skeins?

Multiply the pattern's skein count by its yards per skein for the total, then divide by your substitute's yards per skein and round up. Example: 8 skeins × 200 yd = 1,600 yd; with the 15% safety margin that is 1,840 yd, so a 280 yd substitute needs 7 skeins — not 8.

Can I substitute DK for worsted?

Usually, with adjustments. They are adjacent CYC classes (#3 and #4), so picked from the weight-class dropdowns the calculator rates the swap yellow — “Workable with adjustments” — and adds about 15% extra yardage. The adjustment is a size DOWN, not up: DK is the finer yarn, so the calculator hands back the DK ranges, 4.5–5.5 mm (US 7–I-9) for a hook and 3.75–4.5 mm (US 5–7) for needles, both smaller than the worsted ones, and you swatch there until you hit the pattern's stitch count rather than the yarn's. Yellow is the verdict for two dropdown picks, though. Swatch both yarns and type the measured gauges in and the same swap can come back red, because a four-stitch gap is a different fabric at pattern gauge, not a hook size. Two classes apart (say DK for bulky) is red from the dropdowns alone.

What weight is my yarn if it has no label?

Use wraps per inch: wrap the yarn snugly around a ruler for one inch, count the wraps, and read the class off the chart — 9–11 wraps is worsted, 12–14 sport, 14–18 fingering. The ranges touch at their ends on purpose, and a wrap count that lands on a shared edge is read as the FINER of the two classes: 11 wraps is DK rather than worsted, 14 is fingering rather than sport. The calculator has a WPI mode that does the mapping for you; it is the one method that works for handspun and mystery stash yarn.

How much extra yarn should I buy when substituting?

Add 10% to the pattern total as a baseline, or 15% when you change weight class or work colorwork — then round up to whole skeins while the dye lot still matches. The calculator applies the right margin automatically.

Does fiber matter when substituting yarn?

Yes — elasticity and drape change the fabric even at identical gauge. Wool is springy and blocks to shape; cotton has no memory and grows; acrylic cannot be reshaped by blocking; silk and bamboo drape like liquid; alpaca droops under its own weight. Blends are the safest all-round substitutes, and fiber matters far more for fitted garments than blankets.

Yarn substitution calculator comparing a worsted pattern yarn with a DK substitute, showing a yellow verdict and skeins to buy — Two yarns in — traffic-light verdict, hook and needle range, and skeins to buy out.