Carat (ct)

On the label: Carat · Standard and mark

What it is

The weight unit for gemstones: 0.2 grams. Not karat; a 1 ct diamond weighs a fifth of a gram.

Standard and marks: The marks, tests and laws behind the words on a label: karat stamps, UV400, ANSI Z80.3, the FTC Jewelry Guides, Prop 65.

Wikidata: Unit of mass (200 mg). Q261247 →

In the research

52 PubMed papers mention it with jewelry, allergy, eyewear or UV; the three most recent:

Erratum · International archives of allergy and immunology, 2026
Development and short-term effectiveness of a theory-informed, nurse-led structured rehabilitation consultation in primary care asthma management · Respiratory medicine, 2026
Structural dysanapsis of central airways is linked to inhalant allergen load in patients with asthma: A computed tomography-based analysis from the Hi-CARAT study · Allergology international : official journal of the Japanese Society of Allergol, 2026

A paper is a paper, not a verdict: titles are listed so you can read them, and a study on one fabric or one filter says little about the piece in your hand.

Pieces whose listing names it

24 on the site

Matched from the words in the supplier's listing; the full material line is on each product page.

Oval Lab Grown Diamond Solitaire Pendant

Made in the USA

Jewelry · Charms and pendants

Oval Lab Grown Diamond Solitaire Pendant

Lab grown oval diamond on a 14K gold chain

From $860

Ships in 2 days · arrives in 3–7

Emerald-Cut Lab-Grown Diamond Eternity Ring

Made in the USA

Jewelry · Rings

Emerald-Cut Lab-Grown Diamond Eternity Ring

Emerald-cut lab-grown diamonds set in white gold

$3,399

Ships in 2 days · arrives in 3–7

Made in the USA

Jewelry · Rings

Oval Lab Grown Diamond Eternity Ring

Lab grown oval diamonds set in 14K white gold

$2,554

Ships in 2 days · arrives in 3–7

Made in the USA

Jewelry · Rings

Oval Lab Grown Diamond Eternity Ring

Oval lab grown diamonds in white gold, all the way around

$3,145

Ships in 2 days · arrives in 3–7

Round Lab Grown Diamond Solitaire Engagement Ring

Made in the USA

Jewelry · Rings

Round Lab Grown Diamond Solitaire Engagement Ring

Lab grown diamond solitaire in 14K white gold

$2,131

Ships in 2 days · arrives in 3–7

Made in the USA

Jewelry · Rings

Round Lab Grown Diamond Solitaire Engagement Ring

Classic lab grown diamond solitaire in white gold

$2,131

Ships in 2 days · arrives in 3–7

Three Stone Lab Grown Diamond Engagement Ring

Made in the USA

Jewelry · Rings

Three Stone Lab Grown Diamond Engagement Ring

Three round lab grown diamonds in white gold

$1,286

Ships in 2 days · arrives in 3–7

Round Lab Grown Diamond Three Stone Ring

Made in the USA

Jewelry · Rings

Round Lab Grown Diamond Three Stone Ring

Three lab-grown diamonds in 14K yellow gold

$1,286

Ships in 2 days · arrives in 3–7

Other standard and marks

Karat (k, kt)Fineness (925, 750, 585)Hallmark Mohs hardness scale FTC Jewelry Guides Nickel-free Hypoallergenic Nickel allergy Lead in jewelry Proposition 65 ANSI Z80.3 FDA impact test (21 CFR 801.410)

Clasp & Lens describes materials from the public record and does not appraise, grade or test pieces; what a listing states is the supplier's statement. If a piece causes a rash, take it off; a reaction that spreads or blisters is a doctor's question, and sunglasses are no substitute for impact-rated eye protection where that is required.