Is there a formula for increases when knitting?

Hey everyone,

I need your collective wisdom for a dear friend of mine :-)

She’s knitting a sweater out of leftover sock yarn. The body is finished—now she’s working on the sleeves.
These are knitted flat, have a sleeve cap at the top, and will later be sewn together and attached to the sweater.

She has a gauge swatch.

Right now, the sleeve is 16 cm wide at the cuff and needs to “attach” to the underarm at a width of 52 cm.

Question: Is there a formula for calculating the increases?

Thanks ♥

Oh, my gosh—writing used to be my strong suit... honestly :-)))
So please overlook any weird typos ♥

Well, here’s how I’d approach it:

If she has a gauge swatch, she’d need to calculate how many stitches are needed at the top and how many at the bottom. Then take the difference between those two numbers. Those stitches need to be decreased evenly throughout.

Next, she needs to determine the length of the sleeves and calculate (based on the gauge swatch) how many rows that is. I’d leave out the cuff when measuring.

Then divide the number of rows by half the number of stitches, because 2 stitches are decreased on every decrease row.

This will tell you how many rows to work between the increases.

I hope this doesn’t tie your brain in knots. ;-)

Hey there :) 
Thanks so much! No, I’ve more or less understood it *laughs* and almost worked it out that way too. 
I thought there might be some kind of secret formula where you just plug in the numbers. 
But I guess it’s still the good old rule of three :) 

There’s no secret formula, but the “Knitting Calculator & Abacus” always helps me with the calculations. Try searching for it online. I bought mine at am... It always comes in handy when I need to do the math.