Choosing The Right Size Needles: Squaring Up With Knitpro Cubics

Let me quickly start by pointing out that this is not a sponsored post, and all opinions are entirely my own…

My most recent project on the needles, a pair of socks knit two-at-a-time on a single Knitpro Cubics circular needle, is just the right kind of comfortable stress-free knitting to allow me to dip into and out of an on-going project in rare moments of quiet as Baby Awesome sleeps. Square needles are now available from a number of different manufacturers and many people believe them to both be more comfortable to knit with and to produce more even knitting. I have used wooden Knitpro Cubics to knit items like sweaters, but was tentative at believing that the smaller sized square Nova needles in sizes needed to make socks would be as easy and comfortable to grip: however I have found that they are extremely easy on the hands as the needles do not ‘roll’ as you knit with them, allowing a more relaxed hold.
One of the interesting things to look out for when trying square profile needles such as Knitpro Cubics is the different way that the shape of the needle affects gauge when compared with an equivalent sized round needles. Like normal round needles, square needles are sized by the smallest hole of a needle gauge that the needles will fit through. For a round needle this would be the same as the diameter of the needle, but for a square needle this relates to the size of the needle as measured diagonally from corner to corner. In the example below, both the two needles on the left would fit through the same 8mm hole in a needle gauge, so both are given to be 8mm needles.
However, the distance that the yarn has to travel around the square needle is not the same as the distance that the yarn has to travel around the circumference of a normal 8mm needle.
The circumference of the round 8mm needle is easily found by using πr2 (or π x diameter, for purposes of illustration) and by working backwards through Pythagoras we can easily find the equivalent measurement around the square profile needle. In the example of an 8mm square needle vs 8mm round needle, the yarn has to travel a whole 2.5mm more around the round needle than it does around the equivalent sized square needle. As with anything to do with sizing in knitting, though 2.5mm may seem like a relatively small amount, multiplied up by the many thousands of stitches needed to create a project, this soon becomes a very big disparity.

When trying to achieve gauge for a particular project, many knitters will start their swatching by using the needle size recommended in the pattern. The table below gives the circumference given by commercially available needle sizes and the perimeter of their equivalent sized square counterparts.

Metric Old UK sizing US needle sizes round needle
(circumference) mm
square needle
(perimeter) mm
nearest size
square needle equivalent
Needle size called for in pattern Needle size to try
2mm 14 0 6.28 5.66 2.25mm
2.25mm 13 1 7.07 6.36 2.5mm
2.5mm n/a 1.5 7.85 7.07 2.75mm
2.75mm 12 2 8.64 7.78 3mm
3mm 11 2.5 9.42 8.49 3.25mm
3.25mm 10 3 10.21 9.19 3.5mm or 3.75mm
3.5mm n/a 4 11.00 9.90 3.75mm or 4mm
3.75mm 9 5 11.78 10.61 4mm
4mm 8 6 12.57 11.31 4.5mm
4.5mm 7 7 14.14 12.73 5mm
5mm 6 8 15.71 14.14 5.5mm
5.5mm 5 9 17.28 15.56 6mm
6mm 4 10 18.85 16.97 6.5mm
6.5mm 3 10 1/2 20.42 18.38 7 or 7.5mm
7mm 2 10 3/4 21.99 19.80 7.5mm or 8mm
7.5mm 1 n/a 23.56 21.21 8mm
8mm 0 11 25.13 22.63 9mm
9mm 0 13 28.27 25.46 10mm
10mm 0 15 31.42 28.28 10mm or 12 mm
12mm n/a 17 37.70 33.94 12mm or 15mm
15mm n/a 19 47.12 42.43 15mm or 20mm
20mm n/a 36 62.83 56.57 20mm or 25mm
25mm n/a n/a 78.54 70.71 n/a

Using the table above, a suggested equivalent square needle size is given for each standard round needle, according to which size it falls nearest to. Where an equivalent round needle falls almost equally between two sizes, both are given.

Though the table above can be used to calculate the most likely starting point when trying to achieve gauge, as with choosing the needle for any project, a tension square or swatch should be completed to find the right sized needle for the task in hand. The knitter’s own knitting style and degree of tension when knitting, as well as the varying properties of various yarns, may possibly have an even greater effect on the possible variations in gauge on square needles than they do with round needles. This is due to the fact that the yarn essentially has to travel a path around four corners, rather than a round circumference.
A knitter whose stitches are made under high tension and with a yarn with enough flexibility or drape to cling to the contours of the yarn may find that the disparity in gauge between their use of equivalent square and circular needle is greater than someone with a very relaxed tension, or where a robust yarn with a lot of body and little stretch or drape refuses to conform to the contours of the square needle. Essentially, the looser the yarn travels around the needle, or the more resistant the yarn is to laying tight against the straight edges and sharp corners of the square profile needle, the closer the path of the yarn resembles that which it may take around a regular round needle.

The tension square remains key to achieving correct project gauge when using square profile needles, but using the table given above it may be possible to at least make a best guess at which needle size to start swatching with. Where two sizes are given as close alternatives, ‘tight’ knitters may with to choose the larger of the two sizes, whereas very relaxed knitters may wish to choose the smaller size to begin their test square with.

With so many needle variations on the market from a multitude of different companies manufacturing needles from a vast array of different materials, square profile needles could have been dismissed as just a mere gimmick, but there are many knitters who swear by the needles for both the beauty of the stitches that they produce and the benefits of comfort that they bring to the hand. Some knitters have claimed to be able to knit in comfort and with reduced effects from the pain of arthritic conditions for the first time in years, due to the more relaxed and consistent grip that the needles allow. Whether these beliefs are true or not, square needles can be purchased as interchangeable tips, straight needles, fixed circulars and DPNs from various companies and for not too much money, so it may be worth experimenting with square tips if you experience any discomfort when knitting or, indeed, just want some novelty in your knitting experience – just remember to swatch!