How to Read a Crypto Order Book: Bids, Asks, Spread and Depth
An order book is a live list of resting buy and sell orders for one market. It helps traders see the prices and quantities currently available, but it is not a forecast. Orders can be added, changed, cancelled or filled at any time.
Bids and asks
Bids are buy orders. The highest bid is the highest displayed price a buyer is currently willing to pay. Asks are sell orders. The lowest ask is the lowest displayed price a seller is currently willing to accept.
The highest bid and lowest ask are called the best bid and best ask. If the best bid is 99.90 USDT and the best ask is 100.10 USDT, an immediate buyer would normally interact with the ask side while an immediate seller would normally interact with the bid side.
What the spread shows
The bid-ask spread is the difference between the best ask and best bid:
Spread = best ask - best bid
Using the example above:
100.10 - 99.90 = 0.20 USDT
The percentage spread relative to the midpoint is approximately:
0.20 ÷ 100.00 = 0.20%
A narrow spread may indicate that buyers and sellers are quoting close prices. A wide spread may reflect lower liquidity, higher volatility, a small market or temporary uncertainty. The spread changes continuously and is not the same as a platform fee.
Price levels and quantity
Each row in an order book normally combines a price with a displayed quantity. Several orders at the same price may be grouped into one level. The total displayed quantity near the best prices is often described as market depth.
Depth matters because a large market order may consume several levels. If a trader submits a market buy for more than the quantity available at the best ask, the remaining amount can fill at progressively higher asks. The difference between the expected price and the average execution price is one form of slippage.
A simple depth example
Consider a hypothetical ask side:
| Ask price | Available quantity |
|---|---|
| 100.10 | 2 units |
| 100.20 | 3 units |
| 100.40 | 5 units |
A market buy for 4 units could fill 2 units at 100.10 and 2 units at 100.20. The volume-weighted average price would be:
(2 × 100.10 + 2 × 100.20) ÷ 4 = 100.15
This invented example excludes fees and assumes the displayed orders remain available. In a real market, the book may change before or during execution.
Last price, midpoint and mark price
The last price records the most recent matched trade. It may differ from the current best bid and ask. The midpoint is the average of the best bid and best ask, not necessarily an executable price.
For derivatives, the interface may also display a mark price used for risk controls and liquidation calculations. Do not treat last price, midpoint and mark price as interchangeable.
How market and limit orders interact with the book
A market order seeks immediate execution against available orders. It can move through multiple price levels and therefore does not guarantee one price.
A limit order sets the worst acceptable price. A buy limit sets the maximum price the trader will pay; a sell limit sets the minimum price the trader will accept. If it does not immediately match, it may rest in the book. It can fill partly, remain open or be cancelled before filling.
An order that adds resting liquidity may be treated as a maker order. An order that immediately matches resting liquidity may be treated as a taker order. Fee schedules and exact definitions should be checked on the live platform.
What a depth chart represents
A depth chart is a visual summary of cumulative bids and asks. The horizontal axis usually shows price, while the vertical axis shows cumulative quantity. A steep wall can represent a large displayed quantity at or near one price.
Displayed walls are not commitments to remain in place. Orders may be cancelled, moved or filled. A single wall should not be used as proof that price must reverse.
What the order book cannot tell you
The visible book does not reveal every trader's intention. It may omit hidden or iceberg quantity, activity on other venues and orders that have not yet been submitted. High-frequency updates can also make a static screenshot obsolete almost immediately.
Use the order book as one input alongside trade size, recent executions, volatility and the reason for entering the trade. Avoid treating one moment of displayed depth as a complete view of supply and demand.
Practical reading checklist
- Confirm the exact market and quote currency.
- Read the best bid and best ask before the last price.
- Calculate or estimate the spread.
- Compare intended order size with quantity near the best prices.
- Look several levels deep for possible slippage.
- Distinguish resting orders from completed trades.
- Check whether the book is changing unusually fast.
- Review fees and order conditions before submitting.
Explore the OrangeX.com spot market, review trading-pair basics, compare market and limit orders, and continue learning in the OrangeX.com Academy.
Common questions
Is the best ask the price I will always pay?
No. It is the lowest displayed ask at that moment. A larger order or a changing book can produce fills at several prices.
Does a large buy wall mean price will rise?
No. Displayed orders can be cancelled or filled, and other venues may show different liquidity. A wall is current order-book information, not a prediction.
Why is the last price outside the current spread?
The last price is historical. The best bid and ask may move after that trade, especially in a fast market.
Does a limit order always become a maker order?
Not necessarily. A marketable limit order can immediately match resting liquidity. Check the platform's maker and taker rules.
