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Diamond and Gemstone mm Measurement Chart

Being able to Correctly Measure your Gemstones and Diamonds can help you with 4 Main Issues:

  • Determining Approx. Carat Weight
  • Determining what Size Head you Need
  • Determining if your Stone is Cut Properly
  • Determining what size Stone fits in your Mounting

And, before you can do any of these things, you’ll need these 2 items:

I’ve taken care of the second for you and Created the Most Accurate Measurement Chart there is. Print the Chart out at Full Size, 100%, No Scaling or Up Sizing… Just Print it as is and the Measurements shown on the Chart should be dead on.

The Chart prints to a Full Sheet of Standard Paper.

Get the Chart here…

(P.S. Don’t Print the Images on this Page, Get the PDF and Print that instead!)

Diamond And Gemstone MM Measurement Chart

FREE PDF Diamond and Gem mm Measurement Chart!

Now, before we move on, you’ll also need to know a bit of info:

How to Measure your Stone!

You can’t just Measure a Gem anywhere and get Accurate Results.

You need to know the Proper Positions to get the Right Readings. Like you see below, just about every Shape of Stone is listed as 2 sets of Numbers, like 5×3, 6×4, or 8×10.

2 Spots need to be Measured!

Gemstone MM Measurement Chart

Usually stones are Measured at their Widest Part. If the Stone is Round (and Symmetrical), just one Measurement is usually Sufficient.

But for Fancy Shapes, like the Marquise, Oval, Pear, Princess and Emerald, you’ll need to obtain at least 2 Measurements from 2 Different Sections.

See the Diagram below of the Proper Angles and ways to Measure Diamonds and Gemstones.

How to Measure Diamond MM

Comparing MM Sizes

Once you get the Measurements of your Stone, you’ll be able to look at the Chart you Printed out, and see what the Approximate Carat Weight is.

I say Approximate, because there is no way of being truly accurate with a mm Gauge. You have to actually Weight the Stone on a Diamond Scale to know for sure.

Gemstones are not Perfect. Some are Deep (pretty much ALL Gemstones are Cut Deeper than a Diamond). Some have Thick Girdles, Tall Crowns… Some Stones are Thin and Narrow. They all vary. And without the Actual Depth of the Stone to Factor into the Equation, judging Carat Weight by just the Width is just a Guesstimation!

You can get close, and this is how they do it when they’re Appraising your Jewelry with the Stones still in the Mounting, they Guesstimate according to Standard MM Sizes and what they should be.

MM And Carat Weights

Take a look at the Diamond MM Size Chart Below. It compares MM Sizes to Carat Weights of Diamonds…

Standard MM Diamond Sizes

This Chart can come in real handy if you want to Check the Measurements of your Stone.

Let’s say you are looking to Purchase a One Carat Diamond. You look on the GIA Diamond Report and you see that the Measurements are 6.1 x 6.2.

Note: GIA will usually Measure Round Brilliant Cut Diamonds in 2 Spots, because most Round Stones are NOT Perfectly Round!

Now look at the Charts, you see that a 1 Carat Round Diamond should be 6.5mm. The Diamond at the store is listed as 6.1 x 6.2mm.

What Does this Tell You?

It tells you that your Stone is not as Wide as it should be, which means, it’s Deeper than Normal. The Carat Weight is Distributed more up and down in the Depth of the Stone, than across the Width.

That Stone will not only appear Slightly Smaller than a normal 1 Carat Diamond, but it Probably won’t Shine as much as one either.

Standard Sizes can help you Choose a Better Quality Stone that will have more Brilliance, Sparkle and Fire!

Why Measure Stones?

Jewelers Measure Stones all day long. They have to Determine what Stones will Fit into what Mounting. And for Earrings, they’ll have to make sure Both Stones have the same MM Width (Carat Weights may Fluctuate slightly). Properly Measured Stones will make your Earrings Match (You don’t want a Lopsided Head)! BONUS!

They also Measure Mountings that have Missing Stones to Determine what size fits in the Hole.

They use MM Gauges to tell what Size Head to Order for a Stone. You generally have to order in the next size up, just so the Prongs don’t get Pulled out or Compromised!

Jewelers use Gauges and Charts non stop! It helps them in many ways and finding an Accurate Chart is Imperative!

That’s why I put so much effort into This Chart to make it as Perfect as Possible.

Keep in mind, as I’ve already said, Gemstones like Sapphire, Ruby, Emerald, Garnet, Amethyst and Citrine, will often Weight MORE than a Diamond of the exact same MM width. Gems are Cut Deeper than Diamonds to Enhance and Show off the True Color of the Stone.

Loose Stones Work Perfect!

If you have Loose Diamonds or Gems, simply Print out this Chart and Lay the Stones Face Down on the Sheet. You can Quickly Line them up to the Approximate Carat Weight.

Get your Diamond and Gemstone Measurement Chart Here!

P.S. Just remember to Print it out at Actual Size. No Scaling, No Stretching, No Enlarging, just 100% on a Full Sized Sheet of Paper and you’ll be good to go. :)

Print Diamond Measurement Chart PDF At 100 Percent

Enjoy the Chart!


  1. 1 keerath how many gram in Gemstone?

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