
While I design a lot of my projects, from time to time I use a pattern by a fellow designer. Very rarely though I use recommended yarn, or am able to match the tension. Therefore, in most cases I have to adjust the pattern instructions. There are different methods of doing this.
Reverse engineering and recalculating
This is what I do more often: I use the designer’s numbers to calculate required dimensions of each piece and then do the math to figure the number of stitches, rows etc based on my tension. This method works even better if the designer provides schematics with the dimensions, but not many patterns have that.
Sevilla blouse is a pattern by Mette Wendelboe Okkels (PetiteKnit). The construction is quite simple, and therefore did not require too many calculations. I also used yarn in a very different weight, so redoing the math was the best way.

Pattern calls for a DK weight yarn on 5mm needles, that gives a gauge of 18sts x 27rows in 10cm. I used a sports weight yarn (Laguna – a gorgeous silk noil and cotton blend) and made a decent-sized swatch on 3mm needles. My tension was 22sts x 38 rows.
First I needed to figure out the number of stitches to cast on. The pattern called for 98 stitches. To calculate how many I needed to cast on i used the following formula: I multiplied my gauge (number of stitches in 10cm) by the number of stitches to cast on in the pattern and divided that by the pattern’s gauge (number of stitches in 10 cm in the pattern): (22×98)/18=120 stitches.
If you are familiar with proportions, the gauge/number of stitches formula is as follows:

The same works for rows: to calculate the number of rows to knit for the armholes I multiplied the number of rows per 10 cm in my swatch, by the number of rows to knit for armholes in the pattern and divided by the pattern row gauge. (38×14)/27=20 rows.
I continued using the same formula to adjust all the numbers in the pattern: how many stitches per shoulder and how many for neck, how many short rows for the neck, how many stitches to decrease for sleeves.
It’s not complicated, by requires attention to adjust every step of the pattern. There is one area where the rule of proportion won’t work though – and this is where I often went wrong in my early knitting days. This is when you need to pick up stitches along a vertical edge. This is because the number of stitched to be picked up per row depends on the relation between how many stitches and rows there are in 10 cm. So one needs to pay extra attention, but the principle stays the same: using designer’s row tension, figure out the length of the pick-up edge. Then using you stitch tension, calculate how many stitches you need to pick up. Then divide that number by your count of the rows – and voilà, you know how many stitches per row need to be picked up.
Using a different size from the same pattern

This is an easier way, but it doesn’t always work. It is more convenient when you tension is close to the one in the pattern, and only suitable for pattens written in multiple sizes.
The principle is the following. Using the math above you figure out the number of stitches to cast on for one of the pieces, and then see if any of the sizes of the pattern require the same number of stitches to start. You can then follow the instructions for that size – and not yours, with a few modifications.
This method worked wonders for me when making the Match Cardigan by Caidree. I used some cone yarn I bought many years ago, and swatched on several needle sizes to get the fabric that I liked. I ended up using 5mm needles, so initially I thought I’d have to redo all the math as usual. The measurements suggested I needed size 3. After calculating the number of stitches to cast on, I ended up with the exact number for size 5.
As the pattern is top down raglan construction, I was able to follow the size 5 instructions with minimum adjustments, and the cardigan fits perfectly!
