The math of shrinkage?

Based on how much my guage swatch shrank after washing, how do I estimate how much the finished garment will shrink? Will it be the same ratio (of shrinkage per length)?


[B][B]Below you’ll find the math formula on how to calculate proportion. Felting does not always coincide with the ratio. Heat rubbing and time have to be calculated in. Trial and error play a lot here. Try making two swatches one with the maximum heat and longest spin and another with minimal and you’ll have an average…to use in the proportion you can always shrink a little more each time BUt Not UnshrinK

Good luck
[/B][/B] [B]Proportion[/B]

A proportion is an equation with a ratio on each side. It is a statement that   two ratios are equal. 

3/4 = 6/8 is an example of a proportion.
When one of the four numbers in a proportion is unknown, cross products may be used to find the unknown number. This is called solving the proportion. Question marks or letters are frequently used in place of the unknown number.
Solve for n: 1/2 = [I]n[/I]/4.
Using cross products we see that 2 × [I]n[/I] = 1 × 4 =4, so 2 × [I]n[/I] = 4. Dividing both sides by 2, [I]n[/I] = 4 ÷ 2 so that [I]n[/I] = 2.

Don’t worry about the math. If your swatch is truly representative of the fabric you will be creating in the finished item, you’re all set. Simply treat your swatch as you will your finished item (e.g. washing, hanging, etc.) and check your gauge, measure and count it, and knit accordingly. You don’t have to do any maths, just treat the swatch to get your real/final gauge and knit knowing that is what your gauge is (or will be after washing).

Thanks so much, Gray and Redwitch! What really excellent advice that I wish I had sooner!

Sadly, what I ended up doing is adding extra rows to allow for some length-wise shrinkage, and I didn’t realize until it was ‘too late’ that this resulted in a bigger armhole (doh!), requiring a bigger sleeve. Oops!

On another post I also learned that the sleeve/armhole seam will help stabilize those stitches so they won’t shrink as much.

I’ll have to decide whether to frog the fronts and back to bring the armhole back to correct size, then start the sleeves over again (ouch, just thinking about it is painful).

Well, I’m looking at it as valuable experience!