What is trading pair?

The two assets quoted against each other in a market, written base first, so BTC/USDT prices Bitcoin in Tether.

The pair is the market. An exchange does not list Bitcoin, it lists BTC/USD, BTC/USDT, BTC/EUR and so on, each with its own order book, its own depth, and its own price. Two pairs for the same asset on the same venue can quote differently at the same moment, and arbitrage between them is somebody's business.

What trips people up is assuming that because an exchange supports both their currency and the coin they want, a direct market exists between them. Often it does not, and the buy silently becomes two trades.

How it works

The first asset named is the base and the second is the quote. The price is how many units of the quote buy one unit of the base. Buying the pair means acquiring the base and paying in the quote. Order sizes are expressed in the base, and your balance changes in both.

Which pairs exist is the exchange's decision, driven by where it can find market makers willing to quote. Fiat pairs need banking relationships in that currency, so they are scarcer than stablecoin pairs. A venue may list two hundred assets against Tether and only a dozen against euros.

When no direct pair exists, you route through an intermediate asset, almost always a stablecoin or a major coin. Each leg is a separate trade that pays its own fee and crosses its own spread, and the fills happen at slightly different moments, so the effective rate is not the product of the two headline prices.

Example

Illustrative. You hold 1,000 euros and want a token that trades only against Tether on your venue. Leg one buys USDT with EUR at a 0.10 percent fee and a 5 basis point spread. Leg two buys the token with USDT at a 0.40 percent taker fee and a 20 basis point spread on a thinner book.

Round trip cost is roughly 0.10 plus 0.05 plus 0.40 plus 0.20, about 0.75 percent, or 7.50 euros on the 1,000. The direct EUR pair, had it existed, would have cost you one fee and one spread. Selling later reverses both legs and pays it again.

Why it matters when you buy

The pair you have to use is often a bigger cost than the fee schedule you compared. Before choosing a venue, check that it quotes the coin against the currency you actually hold. The fee comparison shows what each exchange charges, the liquidity data shows which books are deep enough to fill without slipping, and the buy pages list venues by asset and jurisdiction.

Related terms

• spread: the cost of crossing each book
• stablecoin: the usual intermediate asset
• order book: where a pair's orders rest
• liquidity: why some pairs fill better
• ticker: the symbol naming each side
• fiat gateway: how currency enters the venue

Questions

Why is the price different on two pairs for the same coin?

Each pair has its own book and its own participants, so prices drift apart until someone trades the difference away. The gap is usually small on liquid pairs and can be meaningful on thin ones.

Does routing through a stablecoin create a taxable event?

In many jurisdictions yes, because you disposed of one asset to acquire another. The rules differ by country, and the tax pages cover the holding and disposal treatment where we track it.

Which side am I buying?

The base, the first asset named. In ETH/USDC you buy Ethereum and pay USDC, and your order size is quoted in ETH.