Market Depth
The full stack of pending buy and sell orders at every price level — the X-ray of supply and demand behind the quoted price.
Definition
Market depth (also called Level 2 data or the depth of market) is a real-time display of all pending limit orders on both sides of the order book, organised by price level. Rather than showing only the single best bid and best ask, market depth shows the quantity of contracts queued at each of the next five (or more) price levels on each side. This gives traders a forward-looking view of where supply and demand are concentrated, not just the current touch price.
Why it matters
The best bid and ask alone can be misleading about true liquidity. An option might quote ₹100 bid / ₹101 ask with 50 lots at each level — but if there are no orders beyond that, any trade larger than 50 lots will immediately push the price. Market depth reveals this immediately. A deep book with hundreds of lots stacked across multiple price levels can absorb large orders with minimal slippage; a shallow book cannot.
Institutional traders use market depth to time large orders. If you need to sell 500 lots of a Nifty position, you watch the depth on the buy side to see if there are enough resting bids to absorb your sell without collapsing the price. Retail traders use it more tactically — checking whether a large iceberg order (orders that only show a partial quantity) might be lurking in the book.
In fast-moving markets — especially in the last 30 minutes of NSE trading before 3:30 PM IST — market depth can evaporate in seconds. Participants pull their limit orders when volatility spikes, leaving only a handful of lots at each level. This is why slippage is worst near expiry and during news events, even on otherwise liquid contracts like Bank Nifty weeklies.
How it works
NSE's matching engine maintains a centralised order book per instrument. When you request Level 2 data through your broker's API or terminal, you receive up to five bid levels and five ask levels, each with a price and aggregated quantity. For example: Bid side might show 24 lots at ₹150, 18 lots at ₹149.95, 30 lots at ₹149.90, and so on. Ask side might show 15 lots at ₹150.50, 22 lots at ₹150.55, etc. The cumulative quantity at each level tells you the impact cost of trading a given size.
Example
Suppose you want to buy 200 lots of a Nifty ATM call. The depth shows: ask level 1 — 80 lots at ₹200; level 2 — 60 lots at ₹200.50; level 3 — 40 lots at ₹201; level 4 — 30 lots at ₹201.50. Buying 200 lots as a single market order would sweep all four levels, giving you an average fill of roughly ₹200.38. Compared to the ₹200 best ask, you pay ₹0.38 extra per unit — ₹0.38 × 75 × 200 = ₹5,700 in market impact. Splitting the order into tranches over time, or using an algorithmic slice-and-dice approach, reduces this cost substantially.
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