Order book
An order book is the list of limit buy and sell orders for an asset, grouped by price level. It shows how much people are ready to buy and sell at each price.
How it works
An order book has two sides. Bids are buy orders, sitting below the current price. Asks are sell orders, sitting above it. The gap between the best bid and the best ask is the spread. Depth is how much volume sits at each level.
A trade happens when someone takes orders out of the book with a market order. If you buy at market, you take the cheapest sell orders first, then the next ones. If there is little volume, your average fill moves further away: that is slippage.
Traders read the order book to judge liquidity: how easily you can get in and out with size. Large orders can act as temporary support or resistance. But the book only shows intentions, and an order can be pulled in a fraction of a second.
BTC: best bid 60,000 USDT for 0.5 BTC, best ask 60,010 USDT for 0.3 BTC, next ask 60,020 USDT for 1 BTC. The spread is 10 USDT. A market buy of 0.8 BTC fills 0.3 BTC at 60,010 and 0.5 BTC at 60,020, an average of about 60,016 USDT, not 60,010.
In a thin altcoin book, only $2,000 sits between 1.00 and 1.05. A $5,000 market buy pushes the price above 1.05, so you pay noticeably more than the price you saw on the chart.
The biggest mistake is trusting every large order you see. A big "wall" can be spoofing: it is placed to scare or attract the crowd and pulled before price reaches it. Do not rely on one order; watch whether trades actually execute at that level and confirm with the chart and volume. Before a large trade, check the depth and use a limit order so you do not get hit by slippage.
Questions and answers
What is an order book in simple terms?
It is a live table showing how much people want to buy and sell at each price. Sellers (asks) are on one side, buyers (bids) on the other, and the spread sits between them.
How do you read an order book?
Compare the volume on the bid and ask sides, find levels with large orders and look at the spread. A tight spread with plenty of volume near the price means good liquidity.
Why do big orders in the order book disappear?
A limit order can be cancelled at any time. Some large orders are placed only for show, to influence other traders, and are pulled before they fill. This is called spoofing.
Related terms
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Updated: 2026-10-19