The Wacky World of Needle Sizing
Knitting needle sizing can be very confusing, and for good reason. The history behind the development of these systems is pretty wild! As crazy as needle sizes may seem, the system has come together over the years. To truly understand the needle sizing systems, we'll need to look into the history of knitting needles.
Very little has been written on this topic. I had to do a deep dive, scrounging for information across every corner of the web. The best source I found is Susan Webster in Australia. There is also an out-of-print book, "The History of Knitting Pin Gauges" by Sheila Williams. It is considered a rare book, so I had to pass on that. One day, I hope to get lucky and nab a copy.
The first needles invented were straight needles. The British developed the first sizing system based on the Standard British Wire Gauge.
It wasn't until the late 1880s that the US began to develop needle sizing systems, with each manufacturer having a unique system. While the sizes possibly corresponded with something, my best description is random numbers with physical sizes that don't correspond to anything.
Can you imagine if each yarn company had unique needles and sizing systems referenced on their yarn and patterns?
Double-point needles were the only other type available at the time, with a separate sizing system based on the material composition. Steel needle sizes differed from those made from celluloid or bone. Circular needles didn't appear on the market until the early 1900s with the British Aero Twin Pin needles.
Material composition also affected straight needle sizing. Early synthetic "amber" needle sizes differed from those manufactured with bone, wood, and metal needles.
Needle gauges came about because of the size inconsistencies. Each company offered a gauge to size their brand of needles. Eventually, universal needle gauges were created, but fitting all the different sizes and discrepancies onto a single gauge was difficult.
Gauges were especially critical because size markings weren't affixed to needles. One of the early attempts involved tiny pieces of paper pasted to the needle shaft, which didn't work well for obvious reasons.
By the 1940s, knitting had become important, thanks to the war effort. The leading manufacturers of the time were Boye, Susan Bates, and Hero. Eventually, they moved to a standard American sizing system, although Boye insisted on maintaining special sizing for their steel double points.
Metric, US, and UK are today's three basic sizing systems. US sizing was the standard system when we started nearly 30 years ago. Domestic patterns and needles would almost exclusively reference US sizing with no reference to the metric equivalent. The metrics-only references resulted in quite a bit of confusion for American knitters when encountering a foreign pattern.
American needle manufacturers resisted adopting metric standardization even as superior European needles flooded the market. When we began our business in the early 1990s, amid this wave of change, the industry was still working through the kinks of size standardization.
Change was inevitable, and as the yarn world exploded onto the international stage due to the growth of the internet, reconciling the metric and US systems became imperative. The US sizing system doesn't exactly conform to specific measurements, complicating matters.
With both the US and metric systems, as the size numbers get larger, so does the size of the needles. Today, both the US and metric sizes are referenced on needle packaging. The diameter of the needle will be the metric size, with the closest corresponding US size referenced as well. Again, US sizes aren't standardized measurements.
The lack of compatibility between the US and metric systems has resulted in various fractional sizes, such as 1.5, 2.5, 10.5, and 10.75. The corresponding metric size assigned to these fractional needle sizes may differ depending on the manufacturer!
Bottom line - look at the millimeter! The US size can not be relied upon for size consistency.
The UK system is even more confusing in that the sizing numbers run counter to the actual size of the needle. As the sizes get bigger, the UK size number gets smaller. Fortunately, unless you're using an old British pattern, you usually won't have to worry about this!
Needle gauges remain essential because the sizes stamped onto needles can wear off or become hard to read. If you have an older gauge, I recommend getting a new one - especially if it is a Boye or Susan Bates gauge without millimeter sizes listed.
One of my new prized possessions is a round cardboard Boye needle gauge from the 1930's.
I also managed to acquire this rare Boye 7-in-1 Knitamajig. I had never seen one of these before. They are from the 1970's and are supposed to be pretty rare. While neither of these historic gauges is particularly useful, they are a fun bit of history. With knitting needles and gauges, older is never better. Modern tools are usually best.
Today, most needle brands continue making gauges corresponding to their needles. Most modern gauges now include the corresponding metric size, making them universal.