How many stitches?

Still on the subject of my tea cosy in double rib.
Both the patterns I have suggest 49 or 51 stitches for a medium pot. It is worked in double knit wool in a double rib stitch, with the wool used DOUBLE throughout.
I thought I would do it a bit smaller and I cast on 45 stitches and worked one row. It looks enormous! That’s to say it almost covers the needle (size 5).
I think I probably need only half of these stitches, but how do I know? By the way, I don’t actually have the tea pot, as I plan to buy a two-cup one and give it to my daughter with the cosy. I would be happy if it just came out as a small-medium size cosy and then I could search for the pot!
How can I calculate the stitches, especially as this is an elastic kind of stitch?

With just 1-3 rows it probably will seem way big. I would continue on for 3-4 inches and see how it looks then.

After you’ve knit a few more inches, you can measure and see how wide it really is. If your needles are a standard 10" and the sts cover them, that sound about right.

My needles are 15" and I thought they were standard!! In fact all my needles are this length. In fact I’ve never even seen shorter needles than these.
So in view of the fact that my stitches covered 15" I took it all apart and then put on 37 and it seems to be OK (done about 5").