Before the 1940’s needle and hook sizes weren’t as standardized as they are today and companies often didn’t provide a conversion to metric for their sizes either.  From the few gauges that have metric sizes and the Walker’s Bell Gauge which has been measured (see sources), I’ve been able to work backwards and compile metric conversions for historical brand sizes. This chart will be continuously updated as I find more sources/ references especially for older brands. I also own some victorian era needles that I have been able to measure myself.

Download a PDF copy of the charts:

Historical to Modern Size Conversions

Metric (mm)	Walker’s Bell Gauge	UK Needles (older)	US Needles (modern)	US Standard Crochet Hook	US Steel Crochet Hook	Japanese [mm]1
0.5	24		8/02		–
0.625	23		–		–
0.75	22		6/0		14
0.85	21		–		13
0.9	20		–		–
1.0	19		5/0		12
1.15-1.253	18		4/0		11
1.3	–		–		10
1.4	–		–		9
1.5	17		000		8
1.65	16		–		7
1.75	15		00		–
1.8-1.9	–		–		6/5
2.0	14	14	0	0	4/3	0 [2.1]
2.25	13	13	1	B – 1	2	–
2.5	–	12	1 1/2	–	–	1 [2.4]
2.75	12	11/ 12	2	C – 2	1	2 [2.7]
3.0	11	11	–	–	–	3
3.25	10	10	3	D – 3	0	4 [3.3]
3.5	–	9	4	E – 4	00	5 [3.6]
3.75	9	–	5	F – 5		6 [3.9]
4.0	8	8	6	G – 6		7 [4.2]
4.5	7	7	7	–		8
5.0	6	6	8	H – 8		9 [4.8] / 10 [5.1]
5.5	5	5	9	I – 9		11 [5.4] / 12 [5.7]
6.0	4	4	10	J – 10		13
6.5	3	3	10 1/2	K – 10 1/2		14 [6.3] / 15 [6.6]
7.0	2	2	–	–
7.5	1	1	–	–
8.0	–	0	11	L – 11
9.0	–	00	13	M/N – 13
9.5	–	–	14	–
10.0	–	000	15	N/P – 15
12.0-12.75	–		17	–
15-16	–		19	P/Q – 19
19.0	–		35	S – 35
20.0	–		–	–
25.0	–		50	–

Historical Brand Knitting Needle Size Conversions

Metric (mm)	Diadem	Columbia (1918)	Good Shepherd (1918)	Fleisher, A.J.K, VB&H (1918)	Walkers Bell Gauge (1850’s)	British or ‘standard’ Wire Gauge4 [inches]5	American Wire Gauge [inches]
2.0	1	0			14	14 [0.083]	14 [0.072]
2.5	2	1			–	–	–
3.0	3	2			11	12 [0.109]	10 [0.12]
3.25	–	3	1	3	10	–	–
3.5	4	–	–	–	–	10 [0.14]	–
3.75	–	4	2	4	9	–	8 [0.148]
4.0	–	5	–	–	8	–	–
4.5	5	6	4	4 1/2	7	8 [0.18]	–
4.75	–	7	–	–	–	–	–
5.0	7	8	6	5	6	–	4 [0.22]
5.5	9	9	7	5 1/2	5	6 [0.238]	–
6.0	10	10	–	–	6	–	–
7.0	10 1/2	10 1/2	8	6	2	–	–
8.0	11	11	10	7		–	–
9.0	13	13	11	8		–	–
9.5	–	–				2 [3/8″]	0 [3/8″]
10.0	–	15
11.0	15	–

Historical to Modern Steel Crochet Hook Sizes

Metric6	US Steel Size	French Size	English Size7	Walker’s Penelope “Uncotopic”89
0.75 mm	14	26	7
0.85 mm	13	25	6 1/2
1.0 mm	12	24	6
1.1 mm	11	23	5 1/2
1.3 mm	10	22	5
1.4 mm	9	21	4 1/2
1.5 mm	8	20	4	No. 3
1.65 mm	7	19	3 1/2	No. 2.5
1.8 mm	6	18	3	No. 2
1.9 mm	5	17	2 1/2
2.0 mm	4	16	2
2.1 mm	3	15	1 1/2
2.25 mm	2	14	1

Modern Brand Conversion Steel Crochet Hook Sizes

Metric	Standard US steel	Tulip Brand	Clover Brand
0.5 mm		22
0.55 mm		21
0.6 mm		20	12
0.65 mm		19
0.7 mm		18
0.75 mm	14	17	10
0.8 mm		16
0.85 mm	13	15
0.9 mm		14	8
0.95		13
1.0 mm	12	12	6
1.05 mm		11
1.1 mm	11	10
1.15 mm		9
1.25 mm		8	4
1.3 mm	10	7
1.4 mm	9	6
1.5 mm	8	5	2
1.6 mm		4
1.65 mm	7
1.7 mm		3
1.75 mm		2	0
1.8 mm	6
1.9 mm	5	1
2.1 mm	3	0

Brands/ Sources for Tiny Needles

24 - 8/0 - 0.5mm: 
    *Hiya Hiya : ebay or second hand
19 - 5/0 - 1mm:
    *Youmeizer (Amazon) : 5.5"
    Hiya Hiya : 6"
18 - 4/0 - 1.15-1.25mm:
    *Youmeizer (Amazon) : 1.2mm 5.5"
    Hiya Hiya : 6" 1.2mm
17 - 000 - 1.5mm:
     Youmeizer (Amazon) : 5.5"
    *Hiya Hiya : 6" 
15 - 00 - 1.75mm:
    *Hiya Hiya : 6"
14 - 0 - 2mm:
    *Hiya Hiya : 6"

Other "Nonstandard" Sizes:
0.8 mm: 
        *HARFINGTON (Amazon) : 5.5" 
         Youmeizer (Amazon) : 5.5"
0.7 mm:
         Hiya Hiya 8"

*DPN Sock Set: US 000, 00, 0, 1 (1.5mm, 1.75mm, 2mm, 2.25mm)

Notes: None of these links are sponsored. 

Anything with a * next to it I personaly own. 

Sources

Boring But Useful – Knitting Needle Size Conversion Chart by Penelope Hemingway

Confusing bell gauges by Pat Ashforth and Steve Plummer (2020) link

Crochet Hook Sizes by Nancy Nehring link

Early North American Knitting Needle Gauges by Susan Webster link [this one has a bunch of neat photos]

Everyone His Own Knitting Needles by Colleen Formby link

Wire Gauge Chart UK by Francesca Betts link

Riego [de la Branchardiere, Eléanor]. Crochet Book 6th Series, containing D’Oyleys and Anti-Macassars. [c.1850, printed in 1877] link with instructions translated to modern terminology by Kathy Adkins link

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1. Modern Japanese knitting needle sizes increase by 0.3 mm per size, so the actual size is in brackets. The far left metric bracket is just to help with size comparisons. ↩︎
2. HiyaHiya has/ had a set of 8/0 dpn, although I haven't been able to find them for sale anywhere. I got mine second hand. ↩︎
3. These ranges have been consolidated in an attempt to shorten the chart as metric sizes vary within this range but the numbered size generally doesn't ↩︎
4. The wire gauge is one of the first standardized gauges refered to in knitting books in the early 1800's. They are/ were also referred to as 'filiere'. ↩︎
5. The sizes are also in inches as both wire gauges were designed around imperial units, so inches is more exact than the approximate/ rounded metric size. They are placed according to approximate mm for ease of charting. ↩︎
6.  The metric sizes are based on the assumption that the US hooks are the same size today (this is normally a safe guess) ↩︎
7.  I am still looking for a source on the sizes of Penelope Crochet hooks which are referenced in many British patterns from the late 1800’s but don't seem to follow standard English sizes ↩︎
8. This is what I have found when it comes to penelope crochet hooks so far, This source also gives a branded crochet cotton size to match which is also helpful ↩︎
9. I also found a redit thread that aproximates penelope hooks No. 000 as 3.75mm, No.00 as 3.5 and No. 0 as 3.25, however I belive this might just be taken as old UK sizing which is a bit different than penelope sizes. Because I haven't been able to cross reference this as of right now these sizes will not be on this chart. ↩︎