Ring sizing - any jewellers about?

[Asterope]

My husband has just revealed to me that he's bought me an eternity band for an upcoming special anniversary. However, he's in a bit of a muddle because wherever he is buying it from has asked him to be certain of the ring size as the band can't be resized and it's not returnable/refundable. So we've tried a measure they sent, their online measurer and a printed out chart and we seem to get different readings every time. Is there an obvious knack to this or better way to do it. I'm a bit nervous about purchasing this way...

You can order ring size measures from Amazon pretty cheaply. Probably worth it if he’s spending a lot. Does the shop have stores you could go into once they reopen to check for sure?

We have tried the measurer. We must be doing something wrong. We've measured my current rings with a ruler too - we thought I was a J but then the website told us O (he had to put the actual ring on his phone screen). Apparently wherever he's getting it from is entirely online so no actual shops...

Order this if you can, www.amazon.co.uk/DoGeek-Measurement-Scales-Measuring-Diameters/dp/B07FNSHZK8

J and O are very different. You could be making a costly mistake.
Or wait till Monday and head to a jeweller with a ring that fits the right finger and ask them to measure it. You don't need to tell them why. Make out like you're looking at what they sell.

On that link you can use the stick to tell you what size a ring you already have is it use the ring loops to measure your fingers more accurately.

That looks fantastic @Zancah , thank you!

I would also advise going to a jeweller and having your finger measured (or getting them to measure your own ring)
If you're wearing it on your wedding ring finger O, is the upper end of average, J is quite petite.

Also, if you're planning to wear more than 2 rings together, as adding an eternity to an existing wedding/engagement pairing you could probably do to go one size up as more rings together makes them tighter fitting.
Not applicable if you're planning on wearing it on your right hand.

Yes I'm going for the right hand so it'll be on its own. I do have quite small hands - my wedding and engagement rings are Is. But they're a bit on the right side post-kids!

If you're right handed your right hand is likely to be slightly larger than your left, but if you can fit size I rings on your wedding finger (however snugly) I would expect the right hand to be closer to a J than an O.

Thank you @fizbosshoes

Just wanted to update and say the sizer came and I'm a J. I think really I'm an I.5 but the J doesn't come off easily so that's what we're going for. Thanks so much @Zancah and @fizbosshoes for that advice

You're very welcome, so glad you're sorted