A problem with ring sizes

Hello,
I have recently started making silver rings. I make them using blank metal lengths and solder them. I made a couple that ended up being the right size, I'd used a calculation I found that allowed me to find out how long the metal needed to be.
But when it came to me making the rings I'm going to sell I found that the lengths I cut did not make the ring size I needed. I checked and rechecked my calculations and measurements but to no avail.

So I'm wondering if anyone has had a similar issue or knows what I might be doing wrong.

TL;DR. My rings are coming out the wrong size with the right measurements!

Got a worked example?

Actually, even slight filing of the ends to true them up can result in the wrong size, because 1.0mm removed can take it one size down.

You are better off aiming for slightly undersized rings and stretching them to size using an upright ring stretcher. There are some bargains to be found on line. Dennis.

That's a really good idea. Thank you! I didn't really think about how much was coming off the ring when I made it true on the ends. It would explain why the other rings came out fine as I used the right length of metal from the start, it's only when I was having to cut lengths off that it became an issue. I will get one of those. I'm assuming it decreases the thickness of the ring.

Yes, it makes the ring a little thinner, but not so that you would notice.
The secret is to make sure that the metal is annealed and to stretch by not more than one size.

This tool works very rapidly and you could end up with your ring too big. It also has facets as it expands, so your ring needs to be rotated a lot to keep it round.
Lastly with wide rings, you need to turn them over at least once to avoid a tapered shape.

You soon become sensitive to the feel of it and learn how to progress slowly, checking with your ring stick as you go. Dennis.

Up until now, I have had problems spending an inordinate time struggling to true up the ends of rings made from metal cut to the exact length (after creating that strange 'D' shape the tutors tell you to make).
I came across what I call the 'jump ring' method for making rings after watching Andrew Berry's videos on YouTube. Suffice it to say, that after a bit of practice on some copper wire and sheet, I'm now managing to consistently produce rings of the exact size required, using any thickness/width of metal/wire without having to resort to filing, sawing through the edges or the ring stretcher!

I know this method isn't new and has probably been used by others since the dawn of time and makes perfect sense when you think about it, but it was new to me. :)

The links to Andrew's videos are below:

For wire: https://www.youtube.com/watch?v=xaU5acww9gc
For wider rings: https://www.youtube.com/watch?v=sWYa5yxP3pI&t=214s