Three retailers. 2,382 listings. G VS1 Round Excellent IGI.

• All three cells carry a three-retailer Market Median again, and the 1ct Market Median is back: £281. Diamond Labs, 77 Diamonds and Quality Diamonds all cleared the 30-listing minimum at every weight this month. July had only one qualifying retailer at 1ct, so 1ct has no published comparison; 1.5ct fell 9% (£427 to £387) and 2ct 3% (£478 to £466), on the same three retailers both months.
• Prices fell at all three retailers, most at 1ct and 1.5ct. Per carat, ex-VAT, July to August: 77 Diamonds -7% at 1ct (£252 to £234), -9% at 1.5ct (£253 to £229), -3% at 2ct (£238 to £230); Quality Diamonds -6% at 1ct (£284 to £268), -9% at 1.5ct (£237 to £215), -3% at 2ct (£199 to £194); Diamond Labs -1% at 1ct (£205 to £202, against a July figure that was itself below the publication minimum), +7% at 1.5ct (£157 to £168), -2% at 2ct (£162 to £158).
• The price difference is not a quality difference. It is a retailer difference. At 1ct the same G VS1 IGI round costs £242 at Diamond Labs and £322 at Quality Diamonds, an £80 gap; at 2ct the gap reaches £173 on a single stone, identical certification and grade.
• Diamond Labs is still the cheapest retailer at every weight; its figures come from an August 30 collection after its inventory feed returned almost nothing on August 29. The August 29 pull found 1, 4 and 0 listings in the three cells, and a live re-query at the time found only two G VS1 stones in the 1ct band; the next morning the same query returned 74, 268 and 84, with other colours and cuts stocked normally. That is a feed outage at the retailer, not an inventory change, and this edition uses the August 30 collection for Diamond Labs (a one-day gap from the other two retailers, disclosed here and in Methodology).
• What UK buyers assume is a cross-border premium is VAT and exchange rate, not markup. Brilliant Earth UK is excluded from this index: their GBP prices are derived from a USD conversion formula, not independently set for the UK market.
• Three of six audited UK retailers qualified at launch, and the panel is unchanged. London-based Queensmith passed structural eligibility but carries zero G-color lab-grown diamonds. Their inventory is exclusively D, E, and F color, confirmed via live API across all carat bands. A three-retailer result at G VS1 is not a methodology gap. It is the market.
• All prices inc-VAT (20% UK VAT included). Ex-VAT figures are in the methodology section.
• The UK index tracks G VS1, the highest-volume lab-grown specification across UK retailers. The Rings.com US index uses E VS1. Not directly comparable. E commands a color premium over G.

Scope. This index tracks listed retail prices (not transaction prices) across major UK online lab-grown diamond retailers. The August 2026 edition covers 2,382 benchmark-matching lab-grown diamond listings across three retailers. All prices are in GBP, inclusive of 20% UK VAT (inc-VAT). Data was collected on August 29, 2026 (77 Diamonds, Quality Diamonds) and August 30, 2026 (Diamond Labs; see Coverage this edition). This is the fourth edition; the retailer panel is unchanged since the May 2026 inaugural edition.

Coverage this edition. Diamond Labs' inventory API returned almost nothing on August 29: 1 listing at 1ct, 4 at 1.5ct and none meeting the Excellent-cut filter at 2ct, and a live re-query during that collection found only two G VS1 round stones in the 1ct band regardless of cut grade. A re-query on the morning of August 30 returned 74, 268 and 84 qualifying listings, with the retailer's other colours and cut grades stocked normally, so the August 29 result was a feed outage at the retailer rather than an inventory change. This edition uses the August 30 collection for Diamond Labs, one day after the other two retailers; both collections are retained. All three retailers met the 30-listing minimum in all three cells, so every cell has a three-retailer Market Median.

Month-over-month. Per carat, ex-VAT, July to August: 77 Diamonds -7% at 1ct, -9% at 1.5ct, -3% at 2ct; Quality Diamonds -6% at 1ct, -9% at 1.5ct, -3% at 2ct; Diamond Labs -1% at 1ct (July's figure was below the publication minimum, n=15), +7% at 1.5ct, -2% at 2ct. Published Market Medians: 1ct not comparable (July published no 1ct Market Median; June's three-retailer £304 against this month's £281 is -8% over two months on the same three retailers); 1.5ct fell 9% (£427 to £387) and 2ct fell 3% (£478 to £466), each on the same three retailers in both months.

Retailer panel. This edition tracks three retailers: Diamond Labs, 77 Diamonds, and Quality Diamonds. The panel was established in May 2026, when eight retailers were evaluated and three qualified, and it is unchanged for August 2026. Two retailers (Brilliant Earth UK and James Allen) were screened out before formal audit: both price in GBP via USD conversion rather than independently setting UK prices. Six retailers proceeded to formal audit against four criteria: (1) live filterable inventory API with no credentials required, (2) publicly visible per-listing GBP pricing, (3) IGI certification as a filterable and per-listing attribute, and (4) minimum 30 qualifying listings per carat cell. Three qualified. Three were excluded; exclusion reasons are documented in the Excluded retailers note below. The panel is fixed and disclosed for comparability. Any additions, removals, or reclassifications will be explicitly noted in that month's report.

Excluded retailers. Queensmith (queensmith.co.uk) passed structural eligibility criteria but stocks exclusively D, E, and F color lab-grown diamonds: a live API query found zero G-color listings across all three benchmark carat bands, consistent with their premium-positioning sourcing standard. Purely Diamonds (purelydiamonds.co.uk) and Angelic Diamonds (angelicdiamonds.com) are finished jewelry retailers with no loose diamond search inventory.

Price inputs. Prices are the publicly visible list price at the time of data collection. Published figures in the index table include 20% UK VAT applied to the collected ex-VAT price. Ex-VAT medians (per carat) for August 2026: Diamond Labs 1ct £202 (n=74), 1.5ct £168 (n=268), 2ct £158 (n=84). 77 Diamonds 1ct £234 (n=312), 1.5ct £229 (n=840), 2ct £230 (n=402). Quality Diamonds 1ct £268 (n=77), 1.5ct £215 (n=147), 2ct £194 (n=178). The following are excluded: promotional codes, membership discounts, negotiated pricing, and strikethrough compare-at or was-£X reference prices.

Benchmark specification. The benchmark specification is G color, VS1 clarity, round brilliant, Excellent cut, IGI-certified. G color was chosen because it is the highest-volume specification available with consistent depth across the tracked UK retailers. Three weight cells are tracked: 1ct (0.95-1.05ct), 1.5ct (1.45-1.55ct), and 2ct (1.95-2.05ct). Note: the Rings.com US price index uses E color rather than G color. E is a higher color grade and commands a price premium. Cross-market comparisons between the US and UK indices should account for this grade difference.

Statistical method. Each published figure is the median total stone price across all qualifying listings within that cell. Median is used instead of an average to reduce the influence of extreme outlier listings. A minimum of 30 qualifying listings per retailer is required for that retailer's cell to be published, and a Market Median requires at least two qualifying retailers in that cell; a single retailer's price is shown individually but is not published as a market figure. Per-cell sample sizes (n) are visible as tooltips when hovering over any price in the table. Every cell met the retailer threshold this edition.

Deduplication. Listings are deduplicated within each retailer by URL. Stones with identical IGI certificate numbers may appear at more than one retailer and are counted as independent listings at each retailer where they appear.

Data sourcing. The UK index is built from live API queries against each retailer's product inventory backend. All three APIs are public-facing endpoints that power the retailers' own consumer-facing search pages. No credentials, scraper accounts, or private API keys were used.

Market concentration. The UK online lab-grown market is tracked here across three retailers (Diamond Labs, 77 Diamonds, and Quality Diamonds): the primary UK-accessible online retailers with independently-priced GBP inventory and sufficient benchmark-matching stock to produce stable medians across all three carat tiers. A pricing decision by a single UK retailer will move the index median more than an equivalent decision would move the US index.

Comparability. The UK and US indices are not directly comparable: the UK index uses G VS1 and reports in GBP inc-VAT; the US index uses E VS1 and reports in USD. Historical index figures may not be directly comparable when the benchmark specification, the retailer panel, or the set of retailers with published cells changes; this edition's 1.5ct and 2ct Market Medians draw on the same three retailers as July's, and the 1ct Market Median returns after a one-retailer July.

Independence. Rings.com receives no compensation from the retailers included in this index for inclusion or ranking, and no retailer has any editorial control over the methodology or results. This index reflects public list prices only; individual purchase prices may differ due to custom configurations, time-sensitive promotions, or VAT treatment at purchase.