Two sides sit in the book. Bids are offers to buy, stacked from the highest price down; asks are offers to sell, stacked from the lowest price up. The gap between the best bid and the best ask is the spread, and the last price at which a trade actually happened is what most sites display as "the price". Nothing is set by the exchange itself: the number simply reflects the last time two people agreed.
Depth is the part beginners tend to skip, and it matters more than the headline price. Each row of the book shows how much is on offer at that level. A market order fills against the best price first, then the next, then the next, until it is complete. In a book with thick depth a large order barely moves the price; in a thin one the same order eats through several levels and you end up paying an average far worse than the quote you saw. That difference is <a href="/glossary/slippage/">slippage</a>.
This is also why order type matters. A market order prioritises speed and accepts whatever price the book gives; a limit order names your price and waits, accepting that it may never fill. Most <a href="/glossary/centralized-exchange/">centralised exchanges</a> run books like this, while many decentralised venues price trades from pooled reserves instead of a queue of orders. Books can also be misleading, since orders that are not yet filled can be cancelled instantly, so a wall of apparent demand may vanish the moment it is tested.
How to Read a Crypto Price Chart
Key takeaways
- The quoted price is only the last trade, while the book shows what is actually available above and below it.
- Depth decides your real fill price, so the same order behaves very differently in a thick market and a thin one.
- Resting orders can be cancelled at any moment, so a large wall in the book is not a reliable signal of intent.
Order Book — frequently asked questions
What is the difference between a market order and a limit order?
A market order says "fill me now at whatever the book offers", so it executes immediately but the final price is not guaranteed. A limit order says "fill me only at this price or better", so the price is controlled but the order may sit unfilled indefinitely. In thin markets the gap between these two outcomes can be substantial, which is why limit orders are the safer default for larger trades.
Why does the price on the chart differ from the price I paid?
Charts plot the last completed trade, which is a single point rather than a promise. Your order works through the book level by level, so the average price you receive can be worse, especially if the book is thin or the market is moving quickly. Exchange fees are then applied on top. Checking depth before you trade explains most of the difference.
Related terms
Centralised Exchange (CEX)LiquiditySlippageDecentralised Exchange (DEX)Arbitrage All terms →New to crypto, or filling in the gaps? Work through the essentials in Learn, browse every term A–Z, or see live prices for the coins these concepts power.