Worsted weight yarn

They are sold by 25G, 50G etc... that's metric enough for me!!
OurKid1 if you are using a different yarn than the one specified in the pattern, you could find that you don't have enough yarn to finish the project - so I always check the length of yarn in a ball if using something different.

Lengths of yarn in a 50g ball, for instance, can vary quite a lot.

eg Rowan Moordale comes in 100g balls and has 230m in a ball
Patons Smoothie comes in 100g balls and has 200 metres in a ball.
Sirdar Snuggly has 165 metres in a 50g ball

etc

Just found this online OurKid1
airedaleyarns.co.uk/index.php/yarn-count-ply-tickets-guide

The metric count is based on the number of 1000metres in a kilo of yarn. It's shown as for example, 200/1 NM (new metric) or 120/2, 60/2, 30/3, 14/2, or whatever... so the bigger the "big" number the finer the yarn as you get more metres out of a kilo. The second numbers show how many threads the yarn is made up of. This obviously means you have less meterage as you have two threads. So a 200s yarn is very fine and a 60s yarn is fine but a 10s yarn is significantly thicker.
My weaving silks are maybe 60/2 mainly but my weaving Merino (for scarves) is currently a 14/2.
There are numerous systems and they are all still in use to a greater or lesser extent. Different places developed different systems - Yorkshire had it's own wool count for example and I have some old cones labels in YWC !

I didn't know there was a metric system for yarns! They are sold by 25G, 50G etc... that's metric enough for me!! This worsted, sport-weight stuff is American isn't it?

Yarns can be very confusing in my opinion.
I weave and have worsted yarn in many weights! Worsted to me is a type of yarn - smooth yarn with a long staple. Traditionally I suppose it would have been used for making worsted cloth.
I like the metric system for yarns but think it will be years before everyone adopts it.
Sometimes I see yarns for sale and they are not at all what a weaver might expect!

Oh good!

Hope it turns out well

I bought the double knit, using 4mm needles it’s coming out fine.

Thanks for the help

Yes I think so but you could check on Ravelry? And perhaps knit a small test square first - your pattern should have the correct tension for a square.

Yes, but if the pattern wants bigger needles (4.5-5mm) you might have to knit a bigger size to accommodate your DK wool since you're using smaller (4mm) needles. I've done this many times with no problems.

I use dk yarn in place of worsted weight. Light worsted is equivalent to dk, worsted is more like arran. I always do a gague swatch in order to check the tension. I crochet, so I alter the hook size according to the measurements of my swatch.
I hope this makes sense.?