FX volatility measures how much an exchange rate bounces around, expressed as annualized standard deviation of log returns. Developed currencies (EUR/USD, GBP/USD, USD/JPY) typically have 6-12% annual vol — lower than equities (15-25%). Emerging market currencies (TRY, BRL, ZAR) often have 15-25% vol — comparable to equities. Why it matters: A 30% EUR position with 10% FX vol contributes ~3% to portfolio volatility (30% × 10%). This is often underestimated — FX can be a major risk source. Comparison: FX vol is roughly 1/2 to 2/3 of equity vol for developed markets, but similar for emerging markets. FX vol spikes during crises (EUR/USD hit 20%+ vol in 2008).