Order Book Meaning and How to Read Market Depth

An order book is the exchange’s list of pending buy and sell orders for an instrument. Bids are buying prices; offers, also called asks, are selling prices. Market depth shows a view of that book. Your broker may also call its own list of submitted orders an order book. These screens serve different purposes: market depth shows available prices, while the Orders screen shows what happened to your requests.

Read the market-depth columns first

• Best bid: the highest buying price currently displayed.
• Best ask: the lowest selling price currently displayed.
• Quantity: the amount waiting at that price, in the unit the screen specifies.
• Order count, when shown: how many orders make up a price level. It does not identify the traders behind them.
• Last traded price: the price of a completed trade. It can differ from both current bid and ask.

The bid-ask spread is best ask minus best bid. A market buy seeks available sellers; a market sell seeks buyers. The last traded price is not a standing offer to fill your next order.

What "level 5" means and how many levels exist

A "level" here is a price row on one side of the book. Level 5 market depth shows the five best bid prices and the five best ask prices, with the quantity at each. It is the default view in many apps. Searches such as "how many level does orderbook have" are usually asking about this.

So "20-level depth" shown in some apps matches NSE's Level 3 tier, and the full book is available only through the tick-by-tick feed. Whether your app offers 5 or 20 levels is a choice of the broker. Open the depth screen and count the rows to see what you have.

Top of book vs full depth

The "top of book" is the best bid and best ask, which is Level 1. It tells you the current spread. Deeper levels tell you how much quantity sits at worse prices, which helps you judge how far a large order could move the price. Neither shows orders that are hidden through a disclosed-quantity setting, so the visible depth can understate the true size.

Market by price vs market by order

Market by price (MBP) groups all orders at the same price into one row with a total quantity. That is what most depth screens show. Market by order (MBO) lists each order separately, in sequence. MBO is closer to the tick-by-tick book. Any "order count" on a price row is how many orders make up that row, and it can differ between data providers, so do not treat it as the number of traders.

A fictional book you can read across

This made-up order book shows example share prices and quantities. It has no connection to a live company or trading session.

The top buyer offers ₹100.00 and the top seller asks ₹100.10. Their spread is ₹0.10. In a separate small-order example, assume you buy 20 shares at that ask and immediately sell all of them at the unchanged bid. The gross loss is 20 × ₹0.10 = ₹2, before charges.

That loss comes from crossing the spread in this assumed round trip. The example does not mean every order always pays the spread as a separate billed fee. An order might instead rest at a limit price, execute later, execute partly, or never execute.

Why a larger order has a different average price

Using the same fictional ask side, assume a market buy for 150 shares arrives while these orders remain available. The first 50 shares execute at ₹100.10. The remaining 100 execute at ₹100.20.

Average execution price is ₹15,025 ÷ 150 = about ₹100.17 per share. The extra cost against buying the full quantity at the initial best ask is ₹10. Calculate that from the unrounded execution values; multiplying a rounded average back by quantity can introduce a difference.

This is one form of slippage: execution differs from the reference price. In a moving market, actual prices and quantities can also change while the order is being processed. A screenshot can explain an assumption; it cannot establish what liquidity was available when the order arrived.

Price priority, time priority and partly completed orders

NSE’s normal equity matching gives the better price priority. At the same price, earlier orders have priority. An incoming order may execute against several waiting orders; any unfilled quantity remains subject to its conditions. Matching occurs at the waiting order’s price.

A limit buy specifies the highest acceptable buying price. It can match immediately against suitable offers, so limit orders do not always sit waiting in the book. If the limit prevents reaching further sellers, the balance can remain unfilled. A displayed price does not reserve quantity for you.

Read market versus limit orders for the price-control and execution trade-off. Neither an attractive quote nor a chosen limit guarantees that the whole position will trade.

How much of the exchange book can you see?

As checked on 16 October 2026, NSE describes Level 1 data as the best bid and ask; Level 2 includes up to 5 price levels per side, and Level 3 up to 20. Its tick-by-tick feed offers the full order book. Your broker’s display depends on the data and service it provides.

Displayed depth remains different from a list of completed trades. A pending quantity can be matched, changed or cancelled. Disclosed-quantity orders can also expose only part of a larger order. Do not assume the visible rows reveal all remaining buying or selling interest.

For more on the display, see market depth. Check whether any total-buy or total-sell figure refers to the whole pending book or only the displayed rows before trying to reproduce it by addition.

Order book vs trade book in your broker app

The word "order book" has two meanings. The exchange order book is the list of pending orders from everyone. The "Order book" tab in a broker app lists only the orders you placed, with their status. The "Trade book" tab lists only the executions you got.

One order can create several trades. If you send a buy for 150 shares and it fills in two parts, the order book shows one order, and the trade book shows two trades. When you log trades in a journal, use the trade book and contract note for actual prices and quantities, not the order price you typed.

Total buy and sell quantity: why it misleads

Some screens show "total buy quantity" and "total sell quantity". These add up the pending orders, but pending orders can be cancelled or changed at any time, and some size is hidden. A larger total on one side does not predict the next price move. Check what the figure includes, such as all rows or only the displayed rows, before relying on it.

What makes market depth thin or deep

• Liquidity: heavily traded instruments usually have more orders at each price. Rarely traded ones have gaps. See liquidity.
• Time of day: depth can look different around the open and close than in the middle of the session.
• News and events: orders may be pulled or added quickly around announcements.
• Contract choice: a far strike or a far expiry option often has fewer orders than a near one.
• Order size: a quantity that is small for one stock may be large for another.

A thin book means a wider spread and a bigger price move for a given order, as the 150-share example above showed. See bid-ask spread and market depth.

A big order is not a price forecast

A heavy bid can disappear before you sell. A heavy offer can trade and be replaced by another offer. Order counts do not establish how many independent people are involved or whether any order will stay. A single screenshot cannot prove market manipulation or identify a participant’s motive.

For a trade review, record the quote you observed separately from your actual execution. Include the order type, requested quantity, traded quantity and average execution price. That creates a useful explanation of a price difference without treating the earlier quote as a guaranteed fill.

Order book in F&O: an options example

Made-up options book for one strike. Option prices are premiums per unit, and an order must be in multiples of the lot. The example uses a lot of 65 units, as for Nifty.

The spread is ₹118.50 − ₹118.00 = ₹0.50 per unit, which is ₹0.50 × 65 = ₹32.50 for one lot if you buy at the ask and sell at the bid straight away, before charges. A market buy for 2 lots (130 units) would take 65 units at ₹118.50 and 65 units at ₹119.00. The cost is 65 × 118.50 + 65 × 119.00 = ₹15,437.50, an average of ₹118.75 per unit. Option books are often thinner than the index or the stock, so check the depth of the exact strike and expiry. Use a limit order if you want to control the price.

Spoofing and SEBI oversight

Spoofing means placing orders you do not intend to execute in order to mislead others about demand or supply. Exchanges and SEBI have rules against manipulative practices in securities markets. You cannot tell from a single screenshot whether a large order is genuine, so do not assume intent. If you suspect misconduct, raise it with your broker or through SEBI's official complaint channels.

Common order-book questions

Sources

• NSE: equity order matching (checked 16 October 2026).
• NSE: data depth by feed level (checked 16 October 2026).
• Zerodha: order and trade screens (checked 16 October 2026).