Order book
Also called: depth · market depth · order book depth
Definition
An order book is the live list of all open buy orders (bids) and sell orders (asks) for a trading pair, sorted by price, showing how much people are willing to trade at each level.
This entry is shown in English.
How Order book works
Bids appear on one side, usually green, with the highest bid at the top. Asks appear on the other, usually red, with the lowest ask nearest the middle. The gap between the best bid and the best ask is the spread. When a market order arrives, it fills against these resting orders, starting from the best price.
Depth is the amount available at each level. A deep book has large size close to the current price, so big orders barely move it. A thin book has little size, so a moderate market order can push through several levels and cause slippage. Depth charts show the same data as two curves.
Order books change constantly as traders add, cancel and fill orders, and many orders come from market makers and bots. Large visible orders, sometimes called walls, can be cancelled at any time, so do not treat them as guaranteed support or resistance. For your own trades, the book helps you decide whether to use a limit or market order.
Example
Suppose the ask side of a pair shows 2 coins at 10.00, 3 coins at 10.05 and 5 coins at 10.20 USDT. You place a market buy for 8 coins. You fill 2 at 10.00, 3 at 10.05 and 3 at 10.20, paying 20.00 + 30.15 + 30.60 = 80.75 USDT. Your average price is about 10.09, roughly 0.9 percent above the best ask you saw on screen.
Common mistakes
- Placing a large market order without checking how much size sits near the best price.
- Treating a big visible wall as a guaranteed floor or ceiling.
- Reading the last traded price instead of the bid and ask when deciding what you will actually pay.
Learn and practise
FAQ
How do you read a crypto order book?
Bids show what buyers are willing to pay and asks show what sellers want. The best bid and best ask meet in the middle, and the quantities show how much you can trade at each price.
What does a thin order book mean?
It means there are few orders near the current price, so trades can move the price a lot and cause slippage.
Do DEXs have order books?
Some do, such as on-chain order book exchanges, but many DEXs use automated market makers with liquidity pools instead.