Tension swatch woes

[BeBraveAndBeKind]

I am making a cable knit jumper for my friend's baby. The gauge is 21 stitches and 28 rows over 10cm on 4mm needles
over the cable pattern.

I've tried it on 4mm, 3.5mm, 3.25mm and 4.5mm. If the stitch count is right, the row count is way under. The pattern is written as "knit x amount of rows" rather than knit to a certain length.

Is the easiest way round to just work out how many rooms I need for the desired length?

You really do need to get row gauge as, if you don’t, everything in the pattern will look off. Have you tried changing needle material (ie wood instead of metal or vice versa)? That sometimes helps. Is this the yarn that the pattern was written for? Sometimes a yarn just doesn’t work for a particular project. If all else fails, there’s a formula for working out a change of row gauge but it’s a bit fiddly. It’s explained here https://pattylyons.com/2016/11/5-secrets-of-row-gauge/

Thanks @JennieTheZebra@JennieTheZebra. It's not the same yarn - I've switched out Debbie Bliss Cashmerino for Sirdar Cashmere Merino. I thought I'd checked that they were the same tension but I've just double checked and are actually quite different. I think I'm going to find a different pattern.

I didn't know that needle material makes a difference to tension - useful tip for the future. Thank you!