Key Takeaways
- Bids show prices buyers are willing to pay, while asks show prices sellers are willing to accept.
- The best bid is the highest current buy price, and the best ask is the lowest current sell price. Their difference is the bid-ask spread.
- Market depth shows the quantity available across price levels and helps traders estimate liquidity, slippage, and potential price impact.
- An order book only shows currently displayed limit orders. Orders can be filled, changed, or cancelled, so the book cannot predict price direction by itself.
A crypto order book is one of the most useful real-time tools on a trading screen. It shows open buy and sell orders, helping traders see which prices are currently available, whether liquidity is concentrated near the market, and how a larger order could affect its average execution price.
To apply the examples to a live market, you can create a KTX account and open the BTC/USDT spot market on KTX. Check the live price, order type, fee, available balance, and estimated total before confirming an order.
What Is a Crypto Order Book?
A crypto order book is a continuously updated list of open limit orders for a trading pair. It is normally divided into bids and asks and sorted by price priority.
The bid side contains orders from buyers who specify the price they are willing to pay and the amount they want to buy. Higher bids appear closer to the market. The ask side contains orders from sellers who specify an acceptable price and quantity. Lower asks appear closer to the market.
When compatible buy and sell prices meet, the matching engine executes the trade. Filled quantities leave the order book, while new orders, cancellations, and partial fills continually change what is displayed. The order book is therefore a live snapshot rather than a permanent record of demand and supply.
What Do Bid, Ask, Amount, and Total Mean?
| Field | Meaning | What it helps show |
|---|---|---|
| Bid price | The price a buyer is willing to pay | Current buy-side quotations |
| Ask price | The price a seller is willing to accept | Current sell-side quotations |
| Amount | Quantity available at one price level | Liquidity at that specific price |
| Total | Cumulative quantity from the best price | How much depth a larger order may consume |
| Last price | The price of the latest completed trade | Where the most recent transaction occurred |
Price is only one part of the order book. One price level may contain a very small amount or a large group of orders. A trader therefore needs both price and quantity to judge whether an order is likely to execute near the displayed quotation.
How to Identify the Best Bid and Best Ask
The best bid is the highest displayed buy price because it is the most any current buyer offers. The best ask is the lowest displayed sell price because it is the least any current seller accepts.
Suppose an order book shows a best bid of 99.90 USDT and a best ask of 100.10 USDT. A market sell would normally begin matching the bid near 99.90, while a market buy would begin matching the ask near 100.10.
These prices only describe the top of the book. If the available quantity at the best price is smaller than the order, the remaining quantity continues into less favorable levels. The final average execution price can therefore differ from the first quotation.
What Is the Bid-Ask Spread in Crypto?
The bid-ask spread is the best ask minus the best bid:
Bid-ask spread = best ask − best bid
Using the example above, the spread is 100.10 − 99.90 = 0.20 USDT. Traders can also express it as a percentage of the midpoint to compare markets with different price levels.
A narrow spread generally means buyers and sellers are quoting close to one another and the market may be more liquid. A wide spread may reflect lower activity, higher volatility, or limited liquidity. The spread is also an execution cost: buying immediately and then selling immediately could produce a loss even if the underlying market does not move.
How to Read Crypto Market Depth
Market depth describes the quantity available across multiple bid and ask levels. A deep order book can usually absorb a larger order with a smaller change in average execution price. A shallow book may move through several levels quickly.
When evaluating depth, look at the amount near the best bid and ask, how quantity is distributed across adjacent levels, whether one side contains unusually large orders, and how far those orders sit from the current market price. Also watch whether visible liquidity remains in place as price approaches.
A market can have a narrow top-of-book spread but little quantity behind it. In that case, a small trade may execute efficiently while a larger trade still experiences substantial slippage.
How Cumulative Depth Affects Average Execution Price
Assume the ask side contains the following levels:
| Ask price | Available amount | Cumulative amount |
|---|---|---|
| 100.10 USDT | 0.30 BTC | 0.30 BTC |
| 100.20 USDT | 0.40 BTC | 0.70 BTC |
| 100.30 USDT | 0.50 BTC | 1.20 BTC |
A market buy for 1 BTC could fill 0.30 BTC at 100.10, 0.40 BTC at 100.20, and the remaining 0.30 BTC at 100.30. The weighted average price would be 100.20 USDT. Although the best ask was 100.10, the order size consumed multiple levels and produced a higher average price.
This difference is price impact. Slippage is the difference between the expected execution price and the actual average price and can also reflect movement while the order is being processed.
How Order Books Affect Market and Limit Orders
A market order prioritizes immediate execution. It starts at the best available price and continues through the book until the quantity is filled or available liquidity runs out. It normally offers greater execution certainty but cannot guarantee the final average price.
A limit order sets the highest price a buyer accepts or the lowest price a seller accepts. It offers price control but does not guarantee execution. If the best ask is 100.10, a buy limit at 100.10 may match immediately. A buy limit at 99.80 would normally rest on the bid side and wait for a seller. If the market never reaches 99.80, it may remain unfilled.
What Are Buy Walls and Sell Walls?
A buy wall is a bid level with substantially more displayed quantity than nearby levels. A sell wall is a similarly large ask. A buy wall may temporarily absorb selling, while a sell wall may temporarily slow an advance.
Large orders are not permanent commitments. Their owners can modify or cancel them before execution. Rather than treating a wall as guaranteed support or resistance, watch whether it remains as price approaches, whether real trades consume it, and whether new orders replenish the level.
How to Use a Crypto Depth Chart
A depth chart converts cumulative bids and asks into two visual curves. The left side usually represents buy-side depth, and the right side represents sell-side depth. Steeper sections show that more quantity is concentrated within a smaller price interval. Large steps may correspond to visible buy or sell walls.
A depth chart is useful for a quick view of liquidity distribution, but it hides some order-level detail. Use it together with the raw order book, recent trades, and volume rather than as a standalone signal.
How Beginners Can Read an Order Book Step by Step
- Confirm the pair. BTC/USDT means BTC is priced and traded against USDT.
- Locate the best bid and ask. They are the prices closest to the center of the book.
- Check the spread. This indicates part of the cost of immediate execution.
- Review top-level quantity. Compare the planned order size with liquidity near the best price.
- Examine cumulative depth. Estimate whether the order may consume several price levels.
- Choose an order type. Balance execution speed against control over price.
- Verify the fill. Review average price, filled amount, remaining quantity, and fees.
What Are the Limitations of an Order Book?
An order book shows displayed orders, not every participant's full intention. Some traders use hidden orders, iceberg orders, or algorithms that split a larger trade. Visible orders can also be cancelled before execution.
Each trading venue has its own liquidity. The same pair can have different prices, spreads, and depth elsewhere. Use the book on the venue where the order will actually be placed. Treat it primarily as an execution tool rather than a prediction engine.
FAQ About Crypto Order Books
What do green and red mean in an order book?
Many interfaces use green for bids and red for asks, but colors are a design convention. Confirm the Bid, Ask, Buy, or Sell labels on the platform.
Is the best bid the same as the last price?
Not necessarily. The last price comes from the most recent completed trade, while the best bid is the highest current unfilled buy order.
Is a smaller bid-ask spread always better?
A smaller spread generally reduces the cost of immediate execution, but available quantity also matters. A large order can still experience slippage if depth is limited.
Does a large buy wall mean the price will rise?
No. The order may provide temporary liquidity, be filled, or be cancelled. A displayed wall cannot guarantee future price direction.
How can traders reduce order-book slippage?
They can reduce order size, use limit orders, trade in deeper markets, or split a large order. A limit controls price but may remain partially filled or unfilled.
Risk Disclaimer
This article is for informational and educational purposes only and does not constitute financial, investment, legal, or tax advice. Order books change rapidly as orders are placed, filled, modified, or cancelled, and displayed liquidity does not guarantee execution. Crypto assets are volatile and trading may involve slippage, fees, and loss of capital. Review live market data and order details, conduct independent research, and trade only within your financial situation and risk tolerance.