The Tonnes column is the most recently published official figure for each country, not an estimate. The Previous column shows the prior month's reported holding. When these two numbers differ, the Change column shows the net purchase (green) or sale (red) in tonnes. A dash means the figure was unchanged.
The % of World bar shows each country's share of the global official stock, scaled against the US (the largest holder at 8,133 t = 100% of the bar). The Reference column is critical: it tells you which month's data is actually shown. Countries like Germany and France report quarterly; China and others sometimes go months without updating, then post step-changes. Always check the reference date before drawing conclusions about recent activity.
Holdings are reported in tonnes, not currency. To value a position, multiply by 32,150.7 troy ounces per tonne and the live XAU/USD spot price. The same reserve figures, plus the spot rate needed to value them, are available as JSON from the XAUS gold price API.