how to work with multi-system gauge

In knitting we list gauge (in patterns, books, swatches, yarn labels, everywhere) as so many stitches and rows/rounds across a 4 inch/10 centimeter square. These are really easy numbers to measure in both inches and centimeters and so this works well. Because of this, patterns must be written for that relationship between inches and centimeters. Often they are not, and it is a particular point of difficulty for many designers, tech editors, and knitters to grasp.

So I know this post is super math-y, but hang in there with me if this is something you struggle with, and by the end, hopefully you’ll be free of the struggle. If not, comment below.

Converting measurements in knitting patterns

My colleagues and I are asked all the time about converting measurements when writing knitting patterns, and why we advise the way we do. The simple answer is that gauge is given over 4 inches and 10 centimeters, which is a 2.5 ratio, so we must use that ratio when we convert to be correct. Here’s why it trips folks up. . .

In knitting patterns, we convert between the two measuring systems, metric and imperial, with a 2.5 ratio, whereas in reality, 2.5 cm does not equal 1 inch; 2.54 cm equals 1 inch. Yet when it comes to converting measurements in knitting, we use a 2.5 ratio – ‘we are less accurate to be more precise,’ as tech editor Tabitha Dukes says in her article on this subject. This concept can confuse a lot of knitters and designers, because it just goes against our natural instinct to get things right, but the reason we do this is actually simple and brilliant, and the best way to get things right.

Gauge matters.

Not surprisingly, the reason is all to do with gauge. In almost all knitting patterns, gauge is given over 10 cm and 4 inches. That is a 2.5 ratio. Gauge is not given over 10.16 cm and 4 inches, which is a 2.54 ratio. Because gauge is given with a 2.5 ratio, meaning that the pattern was designed with a 2.5 ratio, then for knitters to get the lengths and widths they need, that they swatched for, they must use this base ratio, and designers must be sure to write their patterns this way, since they have given the gauge this way.

If patterns were written with gauges given over 10.16 cm, we would all have a hard time measuring these small uneven measurements in our knitting. Don’t let that make you think these small differences don’t matter. When you multiply this .04 difference over all the stitches and rows in your item, it will make a big difference. If a knitter swatches a 10 cm gauge, gets your numbers, but the pattern has been converted with 2.54, the knitter will not get the promised finished measurements, because your gauge is at a 2.5 ratio. So, the gauge given over 10 cm determines the widths and lengths in the pattern, not what it would be over 10.16 cm. If you give gauge over 10 cm and 4 inches, that is a 2.5 ratio, so you must convert with 2.5.

As a knitter.

Think of it this way: stop comparing the two systems, get that relationship between inches and centimeters out of your head. It doesn’t matter.

If your gauge is based on a 10 cm square, you proceed with the pattern working in centimeters, following the instructions, and you will get the size promised in the pattern. If your gauge is based on a 4 inch square, you will follow the inches in the pattern, and get the promised size. Your measuring tape does not matter. What matters is what system you are working in. If inches, then you can only look at stitches and rows over 4 inches; if working in centimeters, then you can only consider stitches and rows over 10 cm. You can't jump between systems - you have to stay in your measurement system.

This is how your gauge is described, and this is what your measurements are based on.

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Being accurate: an example.

It's not accurate if you are looking at a ruler or measuring tape and comparing measurements. But if you measured your swatch in a particular system, it is absolutely precise. So, because gauge is given over 10 cm equals 4 inches, using a 2.5 ratio, we must convert that way throughout the whole pattern to get the correct lengths and widths. If we use a 2.54 ratio, the numbers we got with our gauge swatch will not be what we end up with in our knitting, and we will be upset.

Consider how this plays out – let’s do some math: If you chose to use 4” = 10.16 cm (1" = 2.54 cm) for your sweater pattern, then the entire pattern needs to be written that way and your metric knitters would have to measure their swatch to the 10.16 cm, not 10 cm, which is difficult. If you list the gauge as stitches/rows over 10 cm, all the measurements need to be based on the 1" = 2.5 cm ratio. If you convert measurements using 2.54, then the knitter will be frustrated because their measurements will not be correct, because it is not based on the gauge, as you can see below:

Gauge says 20 sts/24 rows = 4" or 10 cm
Your knitter gets gauge and their swatch measures as you list.
If you tell them to work to a 15" body length (and convert then with 2.54, which would equal 38 cm), their piece will be half a centimeter longer than what the gauge is based on (37.5 cm). It is a small difference, but exponential as the sizes get larger. They will also use more yarn, in any size, because in some gauges, that difference is 1-2 more rounds/rows.

With bust circumference, at the same gauge, a 62" circumference = 310 stitches. If you convert with a 2.54 ratio, your schematic would list those 310 stitches measuring 157.5 cm, but their actual sweater on the needles will only measure (according to the 10 cm gauge) 155 cm, which is a whole inch less, and the knitter would think they did something wrong or that their gauge was off. They would also end up with a sweater the wrong size, and that would be bad.

Keep it simple.

Simply, if your gauge is given as 10 centimeters = 4 inches, in a 2.5 ratio, the pattern must be written to that ratio, and the measurements must be converted that way, to ensure your knitter gets the measurements you promise. Don’t we always say, gauge is everything? You see, converting the two systems with a 2.54 ratio actually will be an error, cause mistakes, and not get the knitter what you intended at all, and will make them grumpy. Converting with 2.54 will not make the pattern more accurate or correct, it will actually make it wrong.

Let me know if this information still snags in your brain. If a video is more helpful to you, we talked about it on Tech Tip Talk at this mark including its effect on taking body measurements, and answering a question on rounding measurements in patterns.