Calculating Decreases! - I've meant to post this for a while now. I'm surprised this info is not in any crochet book I have read. Maybe I am making this harder than it needs to be but this makes sense to me. Does it to you? If not let me know and I can try to explain better.
This works for all stitches stitches: sc, dc, etc. but will make a bit more sense if you understand what a crochet decrease is. So check this out here and look for single crochet, double crochet and more decreases. This works for all patterns that use a basic stitch like single crochet, double crochet etc. but breaks down with patterns that use a combinations of sts and/or are pattern sts like a shell stitch. So that's for another tutorial.
number of stitches – the number of decreases = the number of stitches after the decreases (This is good to know to make sure decreased enough)
Some patterns might give you the number of stitches after the decrease so you need to know the number of decreases.
Number of stitches - number of stitches after the decreases = the number of decreases
(Number of stitches) divided by (number of decreases) = (stitch interval) – 2(the number sts you are crocheting together to remove one sts)=(the # of stitches you make before you dec)
If you have 42sc and the pattern says decreases evenly by 6 stitches
Number of stitches=42
Number of decreases = 6
42-6=36 (Number of stitches after the decreases)
42 Divided by 6 = 7 -2 = 5
Stitch interval = 7
Number of stitches you make before you dec = 5
You need to do (5sc, dec) 6 times to get 36sc
What if the decreases aren’t even?
Let’s say you have 75sc stitches and the pattern says decrease evenly by 10 stitches
Number of stitches=75
Number of decreases= 10
75-10= 65 stitches
number of number of stitches after the decreases = 65
75 divided by 10 = 7 with a remainder of 5
Stitch interval = 7
Still take the 7-2 = 5
Number of stitches before the dec= 5
Since there was a reminder go to Step 3
Since you need 10 decreases and the pattern says evenly and you got a remainder. You will have 5 xtra stitches at the end if you only use 5 stitches before each dec. So your decreases will not be as evenly spaced as possible. So in reality you can do (6sc before each dec) 5 times and (5 sc before each dec 5) 5 times and get the total number of decreases you need.
So then you need to decide how you want to distribute the decreases. I think this really depends on what you are making and the shaping you are trying to create. As well as the stitch you are using. Most likely you want to do it in such away that the decrease do not show.
So for this one alternate the decreases (5sc, dec, 6sc, dec) 5 times should get you the stitch count wanted at the end.
Or you could do (5sc, dec) 3 times, (6sc, dec) 5 times, (5sc, dec) 2 times.
This has been edited 2/4/2008 hopefully to make more sense.