Need help with a gauge

I am just starting a child’s cable knit and hooded sweater for my grandaughter. The tension called for ( 4mm) 24sts and 32rows but in pattern which is cables and knit I happened to have some wool here which is bamboo Ewe but the tension on it says (5mm) and 18sts and 22rows Is it possible to use this? When checking the tension could I just cast on the amount and see how it is widthways and judge the length?
It is just a nice soft yarn and needed to be used up
thanks, sharon

It will come out larger if you use heavier yarn and don’t adjust the sizing.

Are you asking about casting on less or casting on the normal amount and then seeing about the length? If it’s the latter that would work fine I think.

Okay, thanks I don’t think that it is going to work as I tried a couple of different needles and didn’t do the whole pattern but just the cast on and it seems quite a bit wider I was going to cast on the stitches it called for and see what the width would be

You’ll need to knit up just a sample of the cable pattern to see. Bamboo Ewe is slightly thin for a worsted, so it may work. Cast on about 30 sts and knit 2-3" to see what it looks like. If you have to use less than a 4mm to try and get the gauge, then you might consider using a smaller size of the pattern. Doing the cast on sts and just a few rows makes it look a lot bigger than it would be after you knit a whole sweater. And if you use the smaller number of sts in a swatch to see how many sts/inch, then you can multiply that times the measurement you need to see if you can use the smaller pattern size.