All lessons
Pairs, order books and spreads
A price on the screen is not an unlimited offer. Look at how much is available at that price.
Read the side and quantity of an executable quote.
BTC/USDT quotes the amount of USDT for one BTC. Buying the pair exchanges quote units for the base asset. Selling does the reverse. USDT is an asset with its own risks, so a USDT-denominated profit is not automatically a bank-dollar profit.
The best bid is the highest displayed buying price; the best ask is the lowest displayed selling price. Their difference is the spread. Order-book depth shows displayed quantities at price levels, but orders can change or be cancelled before yours arrives.
Crypto liquidity is fragmented across venues and pairs. A chart's last price may differ from the available price for your quantity. Check the timestamp, venue, pair and order size before comparing prices, and separate displayed liquidity from guaranteed execution.
Let’s use numbers · hypothetical example
Hypothetical: bid 99, ask 101, each for 1 token. Buying 1 at 101 and immediately selling at 99 loses 2 before fees. An order for 5 may consume more price levels and cost more.
Keep in mind
Displayed orders can vanish; the visible book is not a promise to fill you.
Your turn
Sketch three bid and ask levels. Calculate a one-token spread, then explain why a five-token estimate needs depth.
A quick check before we move on
At which side does an immediate buyer usually trade?
- Yesterday's close
- Available asks
- Only the midpoint
Check answer
Available asks An aggressive buy consumes sell orders, subject to available quantity and venue rules.
Sources and further reading
Content reviewed: 29 October 2026
Educational material with hypothetical examples. Trading can cause substantial losses. A course, pattern, stop order or past result cannot guarantee a profit or limit every loss. Practise in simulation and check current rules and product terms in your jurisdiction.