Changing Needles sizes how to alter pattern

I am trying to make this afghan (see pattern below) for my grandmother but don’t like the size of the needle. Can I change it to a size 15 or 16? If I do how does that change the number of cast on stiches and the number of balls of yarn? It says to use 2 strands together. Does that mean that it only takes 3 balls of yarn to make the correct length since you are combining yarn?

Lion Brand® Homespun®
Pattern #: khs-watr


SIZE: One Size
Approx 44 inches x 50 inches

size 35 [19mm]
6 balls of 790-329 Homespun Yarn: Waterfall from Lion head

4 sts = 3 inches, using two strands of yarn held together. BE SURE TO CHECK YOUR GAUGE. When you match the gauge in a pattern, your project will be the size specified in the pattern and the materials specified in the pattern will be sufficient. If it takes you fewer stitches and rows to make a 4 in. [10 cm] square, try using a smaller size hook or needles; if more stitches and rows, try a larger size hook or needles.

k1b = knit into back loop
p1b = purl into back loop


Entire throw is worked with two strands of yarn held together.

With two strands of yarn held together, cast on 58 sts.
Row 1 (WS): K1b, p1b, k1b, k 1, p1b, p 1, rep from * to * to last 4 sts, k1b, k 1, p1b, k1b.
Row 2 (RS): K1b, k1b, k 1, p1b, p 1, rep from * to * to last 5 sts, k1b, k 1, p1b, k2b.

Rep Rows 1 & 2 for pat until throw measures 50", ending with pat Row 1. Bind off, working pat Row 2. Fasten off. Weave in ends.

You can use a size 13 and just one strand and you’ll probably get 3 sts per inch which would change the width to about half the size. You’d have to knit a sample to see how many you get and if you like the fabric, that it’s not too loose. The st repeat is a multiple of 4 plus 2 sts, which means you’d have to figure out how many to CO in your gauge to make it the full 44" wide (or 40" if you don’t want it that large), then make sure that number would be a multiple of 4 (like 4 x 30 = 120) then add two stitches.

That seems like a very small afghan to me. Is that what you want? If you aren’t sure, measure out and fold a sheet to 44"x50" to see what it will be like when it’s finished.

I mess around with needle sizes and different yarn weights all the time. I just knit up a sample then adjust the number of cast-on stitches to go along with how my sample compares with the instructions.

What I can’t help with is calculating how much yarn you’ll need. I can’t tell you how many times I’ve messed that up and had to scrounge up some contrasting yarn to crochet a border on something where I ran out of yarn. :aww: Hopefully someone else will come along to help you with that part. (You’re pattern did account for the 2-strands, however, so you’ll definitely need all 6 balls.)

It could probably be longer, but a 45" square throw is pretty large. I made one that size for my son and DIL. They stretch out a lot too.

The pattern gauge is 4 sts in 3" so 58 sts does come out to about 44" wide.

Thanks for clearing that up. (Our family likes them long enough to go from neck to toe with room to tuck under, so I make mine at least 6’ long unless they’re just lap rugs or foot-warmers.)

You must have tall people in your family…