How the gram price is derived
Although Thai shops quote per gram, the global market quotes gold in US dollars per troy ounce. One troy ounce equals exactly 31.1034768 grams, so the pure gold (24K) gram price is the ounce price divided by 31.1034768, converted to THB at the live exchange rate. Lower purities are then a simple multiplication: 22K/916 is the 24K gram price × 0.9167, and 18K is × 0.75.
The Gold Traders Association of Thailand publishes a reference price several times a day, quoted in Thai baht per baht-weight of 96.5% gold. That local benchmark follows the international USD spot price converted at the USD/THB exchange rate.