The base currency is the first currency in a pair and the unit the exchange rate prices. In AUD/USD, the Australian dollar is the base: the rate says how many US dollars one Australian dollar buys. A rising rate means the base currency has strengthened against the quote currency.
Thinking of the base currency as the item being priced makes any rate readable. AUD/USD is the price of one Australian dollar, measured in US dollars, the same way a grocery price tag measures one item in dollars. Whatever happens to the number, it is describing the base currency’s value.
Market convention fixes which currency takes the base position in commonly quoted pairs, and the Australian dollar is conventionally the base against the US dollar. That convention is why financial news reports the Aussie "rising" or "falling" as the AUD/USD number moves.
On Tradergy’s conversion pages the base is always stated explicitly, and every pair links its reverse so the same rate can be read from either side.
Longer read: How to read a currency pair, and why the order is only a convention. The three letters, the order they appear in, and the fact that the same rate can legitimately be written either way round. Where the codes come from and who decides them.
The practical companion to this definition is the currency converter pages.
Related terms
Quote currency · Currency pair · All terms
Primary authority: RBA explainer: exchange rates. Definition reviewed against the authority’s published material; this page is reference information, not advice.
Common questions
How do I know which currency is the base?
It is always the first code in the pair. In AUD/USD the base is the Australian dollar; in USD/JPY it is the US dollar. The rate expresses one unit of that first currency in units of the second.
Does a higher rate mean the base currency is stronger?
Yes, relative to the quote currency. If AUD/USD moves from 0.64 to 0.66, one Australian dollar buys more US dollars than before, so the Australian dollar has appreciated against the US dollar over that period.
Is the Australian dollar always the base currency?
No. Convention decides pair by pair. The Australian dollar is the base against the US dollar and yen, but market convention places the euro and British pound ahead of it, so those pairs are usually quoted as EUR/AUD and GBP/AUD.