Neither, actually.
A well-fitted ring should slide over your knuckle with a little resistance, sit snugly at the base of your finger, and need a gentle wiggle to come back off. That's the sweet spot. Not loose enough to slide off on its own, and not so tight it leaves an indent or refuses to budge by the end of the day.
Your fingers change size every single day
This surprises a lot of people, but your finger size shifts throughout the day depending on temperature, activity, and hydration.
Fingers are at their smallest in the morning. They swell throughout the day, peaking in the evening, especially after exercise or in warm weather. A ring that feels perfect at 9am can feel uncomfortably snug by 9pm.
This is why getting sized first thing in the morning can be misleading. You might get a size that feels great when you wake up but becomes a problem by the afternoon.
The best time to get sized is mid-afternoon, when your fingers have settled into a stable size. If you want to be thorough, get sized a few times throughout the day and use the average as your guide.
How to know if your ring actually fits
It should pass the knuckle test. When you put it on, there should be a small amount of resistance at the knuckle. Not a struggle, just a slight push. Once it's past the knuckle, it should settle comfortably at the base of your finger without spinning freely.
Taking it off should require a gentle wiggle and pull. If it slides off with no effort, it's too loose. If you have to fight it off or your finger looks squeezed, it's too tight.
A ring that's too loose is a real risk. You can lose it. It spins constantly, which is annoying and can cause the setting to rotate out of position. And it tends to slide off in cold water, which is when most people discover it's gone.
A ring that's too tight is uncomfortable. It can cause swelling if you wear it for long periods, and in extreme cases, it needs to be cut off by a jeweller. That's not fun, and it usually means the ring needs repairs afterward.
Wider bands need a bigger size
If you're choosing a wider band, say 2.5mm or above, you'll likely need to go up half a size compared to what you'd wear in a standard band. Wider bands sit differently on the finger. They cover more surface area, which creates more contact and friction, and that makes the ring feel tighter even at the same diameter.
If you're used to wearing thinner rings and you're sizing for a wider engagement ring band, factor this in before you order.
When in doubt, size up
If you're sitting between two sizes, go with the larger one.
A slightly loose ring is much easier to fix than a tight one. Resizing a ring up (making it larger) is usually a straightforward job for a jeweller. Resizing down is also possible, but it involves removing metal, and depending on the design, that can be more complex and costly.
More importantly, a slightly loose ring is just more comfortable to wear every day. And comfort matters when something is on your finger for the next few decades.
A few other things worth knowing
Cold weather shrinks your fingers. Hot weather swells them. If you're getting sized in winter, your measurement might be slightly smaller than what you'd need in summer. Mention this to whoever is sizing you, or get sized again in warmer conditions.
Pregnancy, weight changes, and certain medications can also affect finger size over time. Rings can always be resized later, so don't stress too much about the perfect fit forever. Just aim for a fit that works well for right now.
If you're ordering a ring without being professionally sized, the ring sizer tools and printable guides that jewellers provide are a decent starting point, but always lean toward the larger size when you're unsure.
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Thanks for reading, Jared and Brie