Knitters' Math - When You Just Can't Get Gauge

Sometimes you need to convert a pattern from one gauge to another.  In other words, you want the same size garment, but you want a different number of stitches and rows to the inch or to the centimeter.  Sometimes, you have a pattern and you simply can't get the gauge - for instance, it was originally designed for some unusual yarn that can no longer be purchased.  Sometimes you have a favorite, tried-and-true pattern, and want to knit it in a different yarn and different gauge.

It's not too hard to do the math to convert from one gauge to another.  Lets's go through the basic steps!

1. Make sure the pattern is a good, accurate pattern.  You wouldn't want to risk your time and materials on a pattern where you can't get gauge because the pattern's gauge is just incorrect. 
2. Remember, you still need the materials you have chosen to be appropriate for the garment.  No sense converting a dainty little tank top intended to be knitted with thin yarn into a bulky yarn gauge! 
3. Recalculate some of the critical measurements on the pattern.  For instance, I would definitely divide the stitches across the bust (front + back) by the given gauge and see if the resulting measurement makes sense.  For instance, if the pattern is 100 stitches wide and the gauge in the pattern in 5 stitches per inch for a "Size 36," then the designer was planning a garment 20" wide (100/5) in the front and 20" wide in the back - 40 inches altogether, which really is a lot of extra room.  Would you like to wear something 40" wide if you are 36" around?  Try measuring your favorite sweater.  Ever since the gone-but-not-forgotten wildly oversized sweater craze, there have been patterns floating around with 6-12" inches of ease.  I can't remember a yarn shop customer who liked more than 2" of extra room in a sweater.  Most people are surprised at how little ease they prefer.
4. Always check the body length and sleeve length, as well.  Hand knitters can get pretty casual about those two measurements because they get in the habit of simply measuring the length from the knitting needles, but machine knitters need to know how many rows to knit.  Measuring the knitting hanging down from the machine is little better than a wild guess since the needles are yanking the knitting wider and the weights are yanking it longer. (yes, I know, I had you do that for a neck scarf, but I had you removed the weights first and it was a 6-foot scarf on a machine that doesn't come with a row counter!)  
5. Once you're happy with your pattern, you need a good measurement of your own gauge.  Make a good-sized sample, let it rest, then block and launder it in the same way you will block and wash your finished garment, and then measure it.  I have detailed instructions for a terrific gauge swatch in the beginner video course.  Even very experienced knitters have asked me to show them how I do this swatch, which is marked with the tension dial setting and has lots of places for measuring.  Please don't try to get by with a skimpy gauge swatch!
6. After you knit the gauge swatch, stop and think about how the fabric feels.  Is it tight enough to not be droopy?  Is it too tight and stiff?  Can you see through it?  Was it too hard to knit on that setting?  Just take a minute and make sure you'll be happy with the tension you chose.
7. If you knit that gauge swatch, it's 40 stitches between markers and 60 rows between markers.  To get your per-inch gauge, measure the stitches in inches and then divide 40 by the measurement you get.  For instance, if you get 5-1/4", 40 / 5.25 = 7.6 stitches per inch. 
8. Do the same thing with the rows - divide 60 rows by the number of inches between the row markers. For instance, if you get 5-1/2", 60 / 5.5 = 10.9 rows per inch.
9. Now, if you want to convert that written pattern to YOUR gauge, use this formula:

YOUR gauge / THEIR gauge X THEIR number = YOUR number

To illustrate this formula in #7, suppose their pattern has you casting on 75 stitches and knitting 110 rows.  Their gauge is 5-1/2 stitches and 7-1/2 rows to the inch.

On the knitting machine, let's say your're getting 7 stitches and 10 rows to the inch.

Their gauge for stitches is 5.5.  Your gauge for stitches is 7.  7/5.5 = 1.27.  Take the 1.27 and multiply by the 75 stitches, and you see that you need to cast on 95 stitches instead of 75 stitches.  (Key issue:  one stitch or one row doesn't matter.  If you're going to be brave enough to do this, you will have to round to the nearest stitch).

Their gauge for rows is 7.5.  Your gauge is 10 rows.  10/7.5 = 1.33.  So instead of knitting 110 rows, you would knit 110 X 1.33 = 146 rows.  

Are you a person who prefers centimeters?  Follow these instructions, except measure in centimeters and every place I mention "inches," think "centimeters."  As a matter of fact, I prefer centimeters when the pattern I'm converting is in centimeters or when I'm working with the Knit Leader.