Alright, heeeere we go. Let's roll up our
sleeves and go over how to figure out how much to decrease from hip to
waist and where to put the decreases. Again, we will go slow, and there
are no stupid questions.
Recap: We are doing the math for a theoretical,
no-time-to-knit-a-real-one, sweater. The sweater is worked from the
bottom up, in the round; we are using my measurements because I am
easily talked into such things. We've already done the math up until
the hip, which is where our first decrease will be worked. The gauge is
7 stitches per inch and 13 rounds per inch; at the hip, we have 319
stitches on our needles.

Here are the steps to work out the decreases from hip to waist.
1. Gather your measurements.
My hip circumference is 44"; my waist circumference is 36.5".
2. Determine your preferred ease for this garment.
At my hip, I chose 1.5" positive ease based on how I like to wear similar garments.
3. Add hip measurement to ease to get finished hip measurement of sweater.
44" plus 1.5" equals 45.5" finished hip circumference Note that this is the measurement that would show up on a schematic.
4. Determine how much ease you want at the waist.
Do I want the same amount of ease at my waist as at my hips? I think
I'd like this sweater to follow the curves of my body a bit more
closely than the gentle shaping we talked about last week, so I will
leave the ease the same at the waist as at the hips: 1.5" positive ease.
5. Add waist measurement to ease to get finished waist measurement of sweater.
36.5" plus 1.5" equals 38" finished waist circumference.
6. Calculate how much you need to decrease from hip (widest bit) to waist (narrow bit).
This is the finished hip measurement minus finished waist measurement: 45.5" minus 38" equals 7.5".
7. Determine the number of total stitches to decrease, hip to waist.
This is the result from number 6 above, multiplied by the stitch gauge:
7.5" times 7 stitches per inch equals 52.5 stitches, which we will round down to make a nice even 52.
Now we know we have to decrease 52 stitches from hip to waist to get
that curvy curve with 1.5" positive ease at both hip and waist. To work a gentler curve, use a larger amount of positive ease at the waist and do fewer decreases.
8. Measure the vertical distance over which the decreases will be worked.
We need to know the distance over which we are decreasing—in this
case, what is the distance from hip to waist? Using my measuring tape,
I find that this is 5" on me. So, I have 5" in which to decrease 52
stitches, or 65 rounds (5" times 13 rounds per inch).
9. Decide where to put the decreases in each decrease round.
Generally, decreases are worked on either side of the "side seams,"
which is in quotes here because my theoretical sweater is worked in the
round. One on either side of the "side seam" each side works out to
four decreases per decrease round. 52 divided by 4 equals 13, so I will
need 13 decrease rounds. Length in which to decrease (65 rounds)
divided by number of decrease rounds (13) equals distance between
decrease rounds (5 rounds).
Summary: From hip to waist, I will work 52 decreases over 65
rounds, with one decrease round every 5th round. Each decrease round
contains 4 decreases, one on each side of the "side seam."
And now we are at the waist! Halfway there! Whoo!
Did that help? Remember, there are no stupid questions, so if you
have something to ask, or just something to say, about today's post, feel free to leave a comment. If your fellow posters don't answer you back, then I might put your question into a future Knitting Daily post!

Sandi Wiseheart is the editor of Knitting Daily.
What's on Sandi's needles? I'm working away on the Secret Project. Yes. Still.