Japan Physical Metals Index™
JPMI — 日本現物金属指数
About & Methodology

What JPMI Measures

Mission, structure, and methodology of the Japan Physical Metals Index

Mission

JPMI aggregates real domestic dealer bids, pawn buyback rates, recycler payouts, and peer-to-peer transaction data to produce a live reference price for physical metals in Japan — reflecting retail liquidity, domestic demand, real buy/sell spreads, scrap versus bullion flows, and secondary market premiums.

The index is expressed in JPY per gram — the unit that Japanese retail participants actually use — not USD per troy ounce, which is the convention of a market most domestic holders never directly access.

Index Structure — Three Layers

The JPMI composite is built from three distinct layers of the domestic physical market, each capturing a different tier of price discovery.

RS
Refinery Spot
The upstream institutional floor. What Japan's major precious metal refiners will pay to buy back silver from the public. The most transparent and consistently published domestic price tier.
Tanaka 田中貴金属工業株式会社
Nihon Material 日本マテリアル株式会社
Mitsubishi 三菱マテリアル株式会社*
DB
Dealer / Pawn Bid
The retail exit liquidity layer. What pawn shops and kaitori dealers will pay walk-in customers for physical silver. Reflects real-world liquidation value for ordinary holders — often below RS, but a truer signal of accessible liquidity.
Nanboya なんぼや（運営主体：バリュエンスジャパン株式会社）
Daikichi 買取大吉（運営主体：株式会社エンパワー）
SR
Street Retail
The peer-to-peer premium signal. Actual sold prices for .999 silver bullion coins on Mercari — what buyers willingly pay above refinery rates. When SR diverges sharply upward from RS, it signals retail hoarding, supply tightness, or a demand surge not yet reflected in institutional prices.
Mercari メルカリ
MSPI-B (1oz .999)

Calculation Methodology

The JPMI composite is a weighted average of the three sub-indices. Weights reflect the relative reliability and update frequency of each data source.

// RS — 精錬所買取価格の単純平均 · mean of refinery buyback prices
RS = mean(Tanaka_buy, NihonMaterial_buy)

// DB — 業者・質屋買値の単純平均 · mean of dealer / pawn bid prices
DB = mean(Nanboya_Sv1000, Daikichi_1g)

// SR — メルカリ成約価格の円/g換算平均 · Mercari sold listings converted to ¥/g
SR = mean(sold_price_¥ ÷ 31.1035) // MSPI-B · 1oz .999 bullion only

// JPMI — 固定ウェイト複合指数 · fixed weight composite
JPMI = (RS × 0.55) + (DB × 0.30) + (SR × 0.15)

// フリマプレミアム対精錬所価格 · street premium vs refinery floor
Premium = (SR ÷ RS) − 1

The SR component uses only sold listings for standard 1oz .999 silver bullion coins — no jewellery, no slabs, no numismatic pieces — to ensure like-for-like comparison. This sub-index is referred to as MSPI-B (Mercari Silver Price Index — Bullion). Updated Mon · Wed · Fri at 10:00 JST.

Data Sources & Update Frequency

RS and DB prices are fetched automatically once daily via GitHub Actions, which runs a Python scraper against the public-facing price pages of each source. Prices are stored in prices.json and read by the index page on load.

SR (Mercari MSPI-B) is updated manually every Monday, Wednesday, and Friday at 10:00 JST. Sold listings for 1oz .999 bullion coins are recorded and averaged. Mercari does not provide a public API, so this component requires manual entry.

* Mitsubishi Materials publishes a retail sell price and a savings-scheme buyback rate. Physical OTC silver buyback is not available at their stores. Their retail sell price is included as an RS reference point but is not counted in the RS buyback mean.

Disclaimer: JPMI is an informational index only. It is not financial advice. All data is sourced from publicly available pages and is provided without warranty. Prices may be delayed or unavailable depending on source availability. JPMI is not affiliated with, endorsed by, or connected to any of its data sources, including Tanaka Kikinzoku, Nihon Material, Mitsubishi Materials, Nanboya, Daikichi, or Mercari.