Your Cart is Empty

A magic formula for evenly distributing shaping

August 14, 2014

A formula for evenly distributing increases or decreases.

It’s not really magic. It’s algebra but maths is rather magical, especially when designing (or even altering) patterns means it’s way more useful than you ever believed in high school. 

Sometimes the number of decreases (or increases) you want to do divides neatly into the number of rows you have available. And sometimes it doesn’t. In that case you have to do the decreases at two different rates (one higher and one lower than the average) or end up with a long straight section instead of a smooth diagonal. 

Of course you can figure out how to distribute your shaping via trial and error or by plotting things out on graph paper. The problem with both of those methods is that they’re time consuming, especially when you’re grading a pattern for several sizes. 

I’ve seen a simpler version of this formula in a few places. I think I first came across it in Maggie Righetti’s Sweater Design in Plain English (an excellent resource if you have any interest in designing).

The problem was that it only worked if the difference between your two rates was 2. That will often be the case, but I found myself trying to something closer to a curve and for some sizes the optimum shaping was achieved by decreasing every row and every 4th row. I wanted a formula that would work whatever the difference between the rates was.

There was also a niggling line in Righetti’s book: 

“I’m not enough of a mathematician to know why you divide by 2. Just take my word for it that you do!” (p.179)

Oh I took her word for it, but I wanted to know why. And I figured that if I knew why maybe I could work out whether you could change the formula to work with different rates. 

It turns out that you can alter the formula to work in all cases and in case you also want to know why it works I made a video:

Don’t care about the why? Just plug your numbers into this formula. It will work as long as your lower rate of shaping is lower than the average rate and the higher rate is higher (within reason!). 

A formula for evenly distributing increases or decreases.

And just the version with words rather than references.

A formula for evenly distributing increases or decreases.

I use this all the time when calculating patterns in a spreadsheet. It’s fairly simple to write a formula that will take your available rows and required shaping and work out what the rates of shaping should be and how many times each should be worked. No more trial and error!


Also in Journal

The beginning of a mattress stitch in contrasting yarn
Learn to Knit: Mattress Stitch

March 29, 2023

By following our step-by-step mattress stitch knitting tutorial, you'll learn how to make your seams look beautiful and how best to prepare your knitting so that when you seam it with mattress stitch, it goes smoothly on the first try.
Read More
A white woman sits on the edge of a pavement with a wall behind her, she is smiling and wearing a cream coloured handknit scarf.
How to Knit a Scarf: A Beginners Guide to Scarf Knitting

March 23, 2023

Want a quick and easy beginners tutorial on how to knit a scarf? This garter stitch scarf is easy to knit and requires just 3 skills; casting on, the knit stitch and casting off.
Read More
Learn to knit: the long tail cast-on
Learn to knit: the long tail cast-on

February 03, 2022

The long tail cast on is a great multi-purpose knitting cast on and the perfect place for beginner knitters to start. Learn how to work the long tail cast on and how to estimate the length of yarn needed with our clear step by step tutorial and video.
Read More