Yarn Substitution & Yardage Calculator

How yarn substitution really works

The single biggest mistake crocheters make when substituting yarn is comparing ball counts instead of total yardage. Two yarns can both be labelled "worsted #4" and yet have wildly different yards-per-ball: one gives you 200 yards per 100 g, another gives you 315 yards per 100 g. "3 balls" of the first is 600 yards. "3 balls" of the second is 945 yards — nearly 60% more yarn. If you swap by ball count, you will either run out or drown in leftovers.

The right formula

Always convert to total yards first, then back to balls of the substitute:

total_yards_needed = original_yards_per_ball × original_balls
balls_to_buy = ceil(total_yards_needed / substitute_yards_per_ball)

The ceil() (round up) matters because you cannot buy 3.63 balls — you buy 4. That rounding gives you a built-in safety margin of extra yards, which the calculator reports so you know whether you can relax or whether you should buy one more ball for safety.

Why "same weight number" is not enough

The Craft Yarn Council weight system (0–7) groups yarns by typical gauge, but it does not guarantee identical thickness. A "DK #3" cotton and a "DK #3" cotton-acrylic blend can differ in yards-per-gram by 20% or more. The denser (fewer yards per gram) yarn is physically thicker, so your stitches come out larger and your finished amigurumi grows — even though the labels match.

The calculator checks this for you. If you enter grams-per-ball for both yarns, it computes yards-per-gram for each and warns you when the substitute is meaningfully thicker or thinner than the original. When that happens, pair this tool with the Amigurumi Resizing Calculator to predict the new finished size.

The dye-lot rule

Once you know how many balls to buy, buy them all at once from the same dye lot. Yarn is dyed in batches, and "colour 29" from lot A can be noticeably different from "colour 29" from lot B — especially in reds, blues, and darks. Mixing dye lots in a single amigurumi is the most common cause of a visible colour seam. If you must buy across lots, work two rows from one ball, then two from the other, alternating throughout to blend the difference.

Worked example

A pattern calls for 3 balls of YarnArt Jeans (175 yd / 50 g per ball). You want to use Hobbii Rainbow Cotton 8/4 (186 yd / 50 g per ball) instead. Total yards needed = 175 × 3 = 525 yd. Balls to buy = ceil(525 / 186) = ceil(2.82) = 3 balls. Safety margin = (3 × 186) − 525 = 33 yd, about 6.3% — comfortable, but buy a 4th ball if you tend to crochet loosely. Yards-per-gram are nearly identical (3.5 vs 3.72), so the finished size will match the original.

Crochet Hook Size Conversion Chart

Metric (mm) to US designations, plus the recommended hook range for each yarn weight. Use this as a starting point — your personal tension always decides the final gauge.

Metric	US	Metric	US
2.0 mm	B-1	4.5 mm	7
2.3 mm	B-1	5.0 mm	H-8
2.5 mm	C-2	5.5 mm	I-9
2.8 mm	C-2	6.0 mm	J-10
3.0 mm	D-3	6.5 mm	K-10½
3.3 mm	D-3	7.0 mm	L-11
3.5 mm	E-4	8.0 mm	M-13
3.8 mm	F-5	9.0 mm	N-15
4.0 mm	G-6	10.0 mm	P/Q
4.5 mm	7	15.0 mm	Q
5.0 mm	H-8	5.0 mm	H-8
5.5 mm	I-9	5.5 mm	I-9
6.0 mm	J-10	6.0 mm	J-10
6.5 mm	K-10½	6.5 mm	K-10½
7.0 mm	L-11	7.0 mm	L-11
8.0 mm	M-13	8.0 mm	M-13
9.0 mm	N-15	9.0 mm	N-15
10.0 mm	P/Q	10.0 mm	P/Q
15.0 mm	Q	15.0 mm	Q

Yarn Weight → Recommended Hook

CYC Level	Weight Name	UK / AU	Hook Range	Typical SC Gauge
0	Lace	1 ply	1.5–2.3 mm	36–42 st / 10 cm
1	Super Fine / Fingering	4 ply	2.3–3.5 mm	32–36 st / 10 cm
2	Fine / Sport	5 ply	3.5–4.5 mm	28–32 st / 10 cm
3	Light / DK	DK / 8 ply	4.5–5.5 mm	24–28 st / 10 cm
4	Medium / Worsted	Aran	5.5–6.5 mm	20–24 st / 10 cm
5	Bulky / Chunky	Chunky	6.5–9.0 mm	16–20 st / 10 cm
6	Super Bulky	Super Chunky	9.0–15.0 mm	12–16 st / 10 cm
7	Jumbo	Super Chunky+	15.0–25.0 mm	8–12 st / 10 cm

Frequently asked questions

How do I substitute one yarn for another in a crochet pattern?

Never compare ball counts — compare total yardage. Multiply the original yarn's yards-per-ball by the number of balls the pattern calls for to get the total yards the project needs. Then divide that total by the substitute yarn's yards-per-ball and round UP to the next whole ball. For example, if a pattern needs 3 balls of a 230-yard yarn (690 yards total) and your substitute has 190 yards per ball, you need 690 / 190 = 3.63, so buy 4 balls. Always buy a little extra from the same dye lot.

Why does my finished piece come out a different size when I substitute yarn?

Because two yarns with the same CYC weight number can have different yards-per-gram densities. If your substitute yields fewer yards per gram, it is physically thicker, so your stitches will be larger and the finished amigurumi will come out bigger — even if the ball says "worsted #4" like the original. Check the yards-per-gram of both yarns: if they differ by more than about 15%, expect a size change and use the Amigurumi Resizing Calculator to predict it.

How many extra balls should I buy when substituting yarn?

After matching total yardage and rounding up to whole balls, look at your safety margin (the extra yards from rounding). If the margin is under 5–10% of total yards, buy one additional ball. Gauge swatching, colour changes, and tension differences can easily consume a 5% margin. If the margin is over 60%, you may be buying from a yarn sold in very small put-ups — check whether a larger skein is available to reduce leftovers.

Is this yarn substitution calculator free?

Yes. The calculator runs entirely in your browser, requires no signup, and exports a printable PDF shopping list for free. There is no usage limit.