The ring is the one you were given. The stone is the part you want to change — a quarter carat you have worn for years, and now a one-carat lab-grown diamond to go in its place. Yes, you can keep the ring and change the stone, by mail. What decides the job is not the new diamond. It is the small part that holds it: the head.
Same size as the old stone, and the head is sound: an ordinary re-set, from $79. Bigger than the old stone: a new head made for it, from about $600 with the gold included. The new diamond is not in either figure — you send it, or we source one and quote it as its own line. A jeweler emails you one firm number in writing before anything is started.
Why a bigger stone almost never fits the old head
A head is made for one size of stone. Its prongs are cut to length and seated to grip one girdle, at one height. A diamond that is clearly wider than the one it was made for cannot simply be pushed in. The prongs end up stretched thin and short over the edge of the stone, and a prong that only just reaches is how a stone is lost a few months later. The head is the cheapest part of the ring to replace, and the most dangerous part to cheat.
The numbers show why. These are approximate diameters for a well-cut round diamond:
| Carat weight | Approx. diameter | Against a quarter carat |
|---|---|---|
| 0.25 ct | about 4.1 mm | — |
| 0.50 ct | about 5.2 mm | about 1 mm wider |
| 0.75 ct | about 5.8 mm | about 1.7 mm wider |
| 1.00 ct | about 6.5 mm | about 2.4 mm wider |
| 1.50 ct | about 7.4 mm | about 3.3 mm wider |
| 2.00 ct | about 8.2 mm | about 4 mm wider |
Every stone is different, so a gemologist measures both the old and the new stone here before the quote is written. Fancy shapes — oval, pear, marquise, emerald cut — are measured length by width, and a change of shape always means a head of that shape.
Going from a quarter carat to one carat, the prongs would have to reach across a stone well over half as wide again as the one they were made for. That is not an adjustment. It is a new head, made to your new stone and matched to the metal and karat of your ring so the join does not show. The old head can take a new stone only when it is the same shape and within a fraction of a millimetre of the old size — and then it is the ordinary $79 re-set.
Lab-grown or natural: what changes for the setting
For the setting, nothing. A lab-grown diamond is diamond: the same material, the same hardness, the same weight for its size. A one-carat lab-grown stone and a one-carat natural stone of the same cut measure the same across, and a jeweler sets them the same way.
What does change is on paper. Lab-grown stones are usually sold with a report from a grading lab, and many carry a laser inscription on the girdle. Send a photo of the report, or its number — it saves measuring and tells us exactly what we are handling. It is not required.
Moissanite and cubic zirconia are not diamond, and their carat figure does not translate into a diamond size, because the materials weigh differently. For those, give the size in millimetres, not carats.
Five things to check before you buy the new stone
- Ask before you buy, if you canSend one photo of the ring from underneath and one from the side. That shows the head, the prongs and the shank, and it tells you what the upgrade involves before you have committed to a stone.
- The shank has to carry itA larger stone means a larger, heavier head. On a band that has worn thin at the back, the shank may need rebuilding too — if it does, the quote says so as its own line. Telling a worn shank from a size problem explains what thin looks like.
- Height, and your wedding bandA bigger stone sits higher and wider. Because a new head is made for your stone, it can be made to sit low enough for a band to rest close against it. Tell us you wear a band, and photograph the two rings together.
- Shape, and the pointsChanging from a round to an oval, pear or marquise means a head of that shape. The points of a pear or marquise are its most fragile spots, and they need protecting prongs of their own.
- Halo and side stonesA halo is built around one size of centre stone. A larger centre stone usually means a new halo as well, and that is quoted as what it is — not squeezed in.
What happens to your old diamond
It is yours, and it comes back to you with the ring. A gemologist documents it together with the new stone, so you know exactly which is which. Do not throw it away and do not leave it behind. The stone that came out of your engagement ring is often the best stone for the next piece:
- a pendant or a pair of studs — a mount made for a stone you already own is its own job, from about $600 with the gold
- a right-hand ring, or kept for a child’s ring later
- sold — Bizak & Co. buys diamonds by mail as well, if you would rather have the value
Do not have the new stone forced into the old head. If a counter offers to “open the prongs a little” to fit a bigger diamond, that is the job that cracks a girdle, or leaves prongs too short to hold. If the head has to be replaced, it has to be replaced.
Do not post a loose stone loose in an envelope. Put the new stone in a small zip bag or a folded paper packet inside the box, and tell us in the form that a loose stone is in the parcel. Every shipment travels on a prepaid, fully insured label, tracked, signature required, both ways — how to pack it.
Do not send the ring without the stone details. Carat, millimetres and any report number, if you have them. A guessed size is what makes a quote change later.
What comes back to you
The same things that come with every job here, at no extra charge:
- Both stones documented by a gemologist trained at HRD Antwerp and the ERIJ Foundation, before and after setting
- A written quote before anything is started, and nothing worked on until you approve it
- Ultrasonic cleaning and polishing with the work — it is never sold as an extra
- Your old stone, returned with the ring
- Insured, tracked return in a keepsake box, adult signature required on delivery
- A 12-month workmanship warranty
Timing is the same one to two weeks door to door as most work here. If you ask us to source the stone, that step is the one that turns a firm date into a range, and your timeline is confirmed with the quote.
Questions about upgrading a diamond
Can I put a bigger diamond in my engagement ring?
Yes, and you keep the ring. What usually changes is the head, the small part with the prongs that holds the stone. A head is made for one size of stone, so a clearly larger diamond needs a new head, made to the new stone and matched to the metal and karat of your ring so the join does not show.
How much does it cost to upgrade the diamond in my ring?
If the new stone is the same size as the old one and the head is sound, it is an ordinary re-set, starting at $79. If the new stone is bigger, a new head is made for it, starting at about $600 with the gold included. The stone itself is not in either figure: you either send it, or we source one and quote it as its own line. You get one firm written quote before anything is started.
Is a 1 carat lab-grown diamond the same size as a 1 carat natural diamond?
Yes, if the cut is the same. A lab-grown diamond is diamond: the same material, the same hardness and the same weight for its size, so a lab-grown and a natural stone of the same carat and cut measure the same across. For the setting it makes no difference. Moissanite and cubic zirconia are different materials with different weights, so for those, give the size in millimetres rather than carats.
What happens to my old diamond?
It is yours and it comes back to you with the ring. A gemologist documents it along with the new stone. Many people have the old stone made into a pendant or a pair of studs, or keep it for a right-hand ring; if you would rather sell it, Bizak & Co. buys diamonds by mail as well.
Can you find the new stone for me?
You can buy the stone yourself and send it with the ring, which is what most people do. If you would rather we look for one, say so in the form. A stone we source is quoted as its own line, with its details, and nothing is bought until you approve that line.
Will my wedding band still sit next to the ring?
A bigger stone sits higher and wider, so it can change how a band lines up. Because a new head is made for your stone, it can be made to sit low enough for a band to rest close against it. Tell us in the form that you wear a band, and send a photo of the two rings together.