How to Read the Order Book
To read the order book, treat each level as resting limit orders that can be canceled at any moment. It shows what participants say they will do rather than what they have done, which is why large visible orders are the least reliable part of it.
The order book lists the limit orders currently resting at each price, on both sides. It is the closest thing to a live picture of supply and demand, and everything on it is provisional — an order is an intention until it is filled.
Before you start
An understanding that resting orders are intentions and can be canceled instantly. Nothing on the book is a commitment. That is the fact everything else follows from.
A decision about what you are looking for, because the display updates faster than you can read it. Spread width, depth near the touch, or size at a specific level. One question.
An instrument liquid enough that the book means anything. In something thinly traded the book is a handful of orders and tells you very little.
The steps
1. Read the spread first
The difference between the best bid and the best ask is what a round trip costs you immediately. Say the bid is $50.00 and the ask $50.02: buying and selling straight back costs $0.02 a share, or $2 on 100 shares, before commission.
2. Look at depth near the touch, not far from it
Size resting a few ticks away is what your order will actually interact with. Orders twenty levels out are unlikely to be there by the time price arrives.
3. Treat large visible orders with suspicion
An unusually large order sitting where everybody can see it is the easiest thing in the market to cancel. Genuine size is frequently hidden precisely to avoid this.
4. Compare the book against actual trades
The book says what people intend; the trade record says what happened. When the two disagree, the trade record is the one that already occurred.
5. Check your own size against the depth
If your intended order is a meaningful fraction of what is resting, you will move the price yourself. In that situation the book is describing a market you are about to change.
6. Do not place stops at visible clusters
Levels where orders visibly pile up are exactly the levels worth reaching. Placing yours a little beyond the obvious concentration costs a small distance and removes you from the queue.
7. Take structural levels from the chart, not the book
The book shows this instant. A level price has respected three times over a month is a different kind of evidence, and it is the kind that survives the next thirty seconds.
How to tell it worked
The spread was checked before every entry, in every case.
Your order was less than 10 percent of the depth at the levels it would consume.
0 stops were placed at a visible order cluster.
And structural levels came from the chart, with the book used only for execution decisions.
Why the visible book is incomplete
A great deal of size is hidden. Iceberg orders show a small portion and refill; other order types do not display at all. What you see is a subset, and not a random one.
And it is one venue’s book. Trading is fragmented across many venues, so the depth on your screen is a slice of the total rather than the whole picture.
What it is genuinely useful for
Deciding how to execute. Whether to use a limit or a market order, and whether your size will move the price. Those are answerable from the book and hard to answer without it.
Measuring the real cost of a trade. The spread and the depth together tell you what entering and leaving will cost, which is the arithmetic most methods ignore.
And nothing predictive. The book is a snapshot of stated intentions that can vanish in a moment, and treating it as a forecast is reading a queue as a commitment.
Who is actually on the other side
Market makers quote both sides continuously. They are not expressing a view about direction; they are earning the spread and managing the inventory that accumulates from doing so.
Which means most of the depth near the touch is not opinion. It is a business being run, and it adjusts to inventory and volatility rather than to any belief about where price is going.
Genuine directional size usually hides. A participant who actually wants to accumulate has every incentive not to advertise it, so the orders that most reflect conviction are the ones you cannot see.
That inverts the naive reading of the screen. The visible size is largely mechanical, and the conviction is largely invisible — which is why the book answers execution questions well and directional ones badly.
The original data
Of the 24,971 unique videos in the finance search study this site keeps, 3 mention the order book in the title, at a median of 2,367 views across 3 channels, and only 1 of the 3 is instruction-shaped. Time and sales and depth charts return 0 mentions each. Every figure counts each video a single time.
3 videos in 24,971 on the mechanism every single order interacts with. The entire microstructure group — book, tape, depth — has almost no instructional coverage, while the strategies that execute through it have thousands of videos.
The question: A very large bid is sitting 3 ticks below. Buy against it?
The answer is that a large visible bid can disappear before price reaches it. Buying against it is trusting an intention — and the larger and more visible it is, the more reason there is to doubt that it will still be there.
When it fails
The failure is treating a large resting order as support, and it is the book’s most expensive illusion. A substantial bid appears a few ticks below, which reads as a floor. A position goes on against it with a stop just underneath. As price approaches, the order is canceled — it cost nothing to place and nothing to withdraw — and the level that justified the entire trade evaporates in the moment it was supposed to matter.
The second failure is reading depth far from the touch. It will not be there.
A third is oversized orders. You become the price movement.
A fourth is stops at visible clusters. They are worth reaching.
A fifth is treating one venue’s book as the market. Trading is fragmented.
And a sixth is using it predictively. It is a snapshot of intentions.
Related
Order book covers the structure in detail. Level 2 is the common name for the display. And depth of market is the aggregated view of the same data.
The lesson was that a large order sitting on the book is not support. It is a message, and it can be canceled the instant price gets close. What actually happened is in the trade record, not in the list of things people say they might do.
— Michael Whitman
This page is educational, not financial advice. Test every idea on your own charts before risking money.