# Creating Knitting Patterns, Day 6: Knitting Calculations

Welcome to Day 6 of the Complete Guide to Creating Knitting Patterns series! Today, we are going to talk about knitting calculations.

## First Things First: Gauge

We learned details about knitting gauge in an earlier post this year already. Based on the swatch you knitted yesterday, the most important thing in knitting calculations is to determine your gauge: determining the number of stitches and rows per inch.

Sometimes your gauge is referred to by stitches in 4 inches, or in 10 cm, or even stitches per cm – it all boils down to the same thing. Please refer to the article about knitting gauge for details.

When I’m talking about “unit” widths and heights below, I’m referring to whatever one unit is in your preferred system: for me, a unit width is 1 cm. For you, it might be 1 inch. Take whatever you prefer.

Measure the width (= W) and height (= H) of your swatch and count both rows (= r)  and the number of stitches (= s).

My example swatch measures 32 stitches (= s) and 40 rows (= r) in 14 (= W) by 12 cm (= H).

Calculate stitches per unit width (SPU) and rows per unit height (RPU) as follows:

`SPU = s/W = 32/14 = 2.3 sts per cm`
`RPU = r/H = 40/12 = 1.7 rows per cm`

So now you know how many stitches you need to cast on to reach a width of one unit.

In my example, I need to cast on 2.3 stitches for each cm of width I want to achieve; and work 1.7 rows to result in one cm in height.

How Many Stitches to Cast On?

Define the width (or circumference) of the part you intend to knit (= A), then calculate the number of stitches to cast on (= CO) by

`CO = A * SPU`

and round to whole numbers.

As an example, I use a knitted hat for a head circumference of 58 cm. My number of stitches per cm (SPU) equals 2.3 stitches per cm, so I need to cast on

`CO = 58 * 2.3 = 133 sts`

Yes, it is that simple.

The same principle applies to calculations of how many rows to knit for any desired height – just multiply the desired height (= B) by the number of stitches per unit height (RPU),

`ROWS TO WORK = B * RPU`

and you’re done.

## Exercise: Calculate The Numbers For Your Selected Stitch Patterns

Knit a swatch for each of your selected stitch patterns (if you haven’t done already) and calculate your number of stitches to cast on. Go and get some practice now, and let me know how it goes by leaving a comment below!

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