Rapaport Diamond Trade Index
Rapaport Diamond Trade Index
Transaction-derived benchmarks tracking polished-diamond values across size categories
The Rapaport Diamond Trade Index (RAPI) is a suite of price indices for polished round-brilliant diamonds, published by Rapaport USA Inc. as a complement to the firm's better-known weekly Rapaport Price List. RAPI is intended to provide a transaction-orientated benchmark of polished prices across selected size and quality bands, derived from activity on the firm's RapNet trading platform and updated more frequently than the wholesale price list itself. The indices are widely cited in trade reporting on diamond market trends and serve as reference points in some price-linked contracts.
Composition of the indices
RAPI is published in size-band tranches that correspond to commercially significant categories. Standard published indices cover round brilliants in the size bands 0.30 to 0.39 carat, 0.50 to 0.69 carat, 1.00 to 1.49 carat, and 3.00 to 3.99 carat, among others, with each index tracking a representative basket of colour and clarity grades within that band. The RAPI 1.00 — the index for one-carat round brilliants — is the most widely cited single number in trade reporting because the one-carat round at common bridal-market grades is the diamond industry's reference unit.
Rapaport publishes the indices on a regular schedule with monthly and quarterly updates that summarise price movement against historical baselines. The indices are reported as percentage changes and as index levels relative to a reference base period.
Methodology
Rapaport derives RAPI values from RapNet, the firm's online business-to-business trading platform on which diamond dealers list inventory with asking prices, certificate references, and detailed specifications. The methodology incorporates median or trimmed-mean asking prices for stones meeting the index criteria, with adjustments for market discount conventions. The result is a number that approximates the trade's working price for the index basket on a more current basis than the formal weekly price list permits.
The indices are subject to the limits inherent in their data source. RapNet listings are asking prices rather than transaction prices, and the platform sees a substantial but not exhaustive share of global diamond trade flow. Where actual transaction prices and RapNet asking prices diverge — as they sometimes do during periods of rapid market movement — the indices reflect the asking-price view of the market rather than the realised-trade view.
Position in the trade
RAPI complements the weekly Rapaport Price List, which has been the global benchmark for round-brilliant pricing since 1978 and which serves as the structural reference for the discount-to-Rap convention by which the trade quotes prices ("-12% back of Rap" being a typical formulation). Where the price list provides an asking-price grid issued weekly across the full colour-clarity matrix, RAPI provides higher-frequency tracking of selected representative tranches and a more transaction-orientated view of recent price movement.
Both RAPI and the underlying price list are products of the Rapaport Group, founded by Martin Rapaport in 1978. Use of the price list and RapNet platform requires subscription, and access to detailed RAPI data is part of the broader Rapaport service. The trade has a complex relationship with the Rapaport publications — they are simultaneously the standard reference and a subject of periodic dispute about methodology — but their position as the dominant pricing reference for the wholesale round-brilliant trade is firmly established.
Use in contracts and analysis
RAPI is used in some long-term commercial contracts as a price-adjustment reference, for example in arrangements between rough-diamond producers and their polished-diamond customers where polished-price movements partially determine forward rough pricing. Trade research and journalism cite RAPI movements as evidence of market direction, and producers' financial disclosures sometimes reference RAPI in discussion of polished-market conditions.
For academic and commercial analysis, RAPI is one of the few publicly cited diamond price indices. Other index providers — Polished Prices, IDEX Online, and HRD's index suite among them — publish competing benchmarks with different methodologies and data sources. Analysts comparing the diamond trade across periods typically draw on more than one of these series.
In the trade
For dealers, RAPI levels are routine reference points in monthly and quarterly trade reporting. The numbers are not directly used in transaction quotation — the trade quotes against the weekly price list — but RAPI movement informs expectations about the direction of the price list and the market generally.