Reading the order book without over-reading it
Advanced9 min readUpdated February 2026
What the book actually shows
The order book is a snapshot of resting limit orders at each price level. It tells you where liquidity currently sits and roughly how much size a market order would consume before moving the price. That is genuinely useful information about cost.
What it does not show
Resting orders can be cancelled instantly and frequently are. A large bid sitting three levels below the market is a statement of intent that costs nothing to withdraw. Treating visible size as a floor under price is one of the most common ways traders misread depth.
- Use depth to estimate execution cost for a given size.
- Compare book size to the trade tape — prints are commitments, quotes are not.
- Expect depth to thin dramatically in the seconds around a data release.
Book plus tape
The time-and-sales tape records what actually traded. Read the two together: the book tells you what is on offer, the tape tells you what people were willing to pay for. Disagreements between them are usually more informative than either alone.
This material is educational and does not constitute investment advice. Trading leveraged products carries a high level of risk and can result in the loss of your capital.