# Order-book depth and spread: reading the liquidity behind a quote

An order book lists bids to buy and asks to sell at specified prices and sizes. The spread is the gap between the best bid and best ask. Depth measures the quantity available across price levels; a trade larger than the best level can execute at several prices and have a worse average than the top quote.

Evidence: [Interface of the Trade tab](https://help.dydx.trade/en/articles/166979-interface-of-the-trade-tab); [Perpetual order types on dYdX Chain](https://help.dydx.trade/en/articles/166981-perpetual-order-types-on-dydx-chain)

Canonical: https://degreesofsatoshi.com/encyclopedia/order-book-depth-spread/
Published: 2026-10-02
Substantively modified: 2026-10-02
Independently verified by an automated reviewer: 2026-10-02T19:18:00.092Z
Data current through: 2026-10-02

AI-assisted research and drafting with a separate automated source-verification pass; no external expert or named human review is implied.

## Key facts

- **Bid:** A bid is a resting offer to buy. ([Interface of the Trade tab](https://help.dydx.trade/en/articles/166979-interface-of-the-trade-tab))
- **Ask:** An ask is a resting offer to sell. ([Interface of the Trade tab](https://help.dydx.trade/en/articles/166979-interface-of-the-trade-tab))
- **Depth chart:** The chart aggregates orders by price level. ([Interface of the Trade tab](https://help.dydx.trade/en/articles/166979-interface-of-the-trade-tab))

## Walk through the available asks

Imagine the best bid is 99 B and the best ask is 101 B per A. The spread is 2 B. If asks offer 3 A at 101 and 4 A at 102, buying 5 A would cost 3 × 101 + 2 × 102 = 507 B before fees, an average of 101.4 B per A.

The 101 quote describes only the first available level, not all five units.

Evidence: [Interface of the Trade tab](https://help.dydx.trade/en/articles/166979-interface-of-the-trade-tab); [Perpetual order types on dYdX Chain](https://help.dydx.trade/en/articles/166981-perpetual-order-types-on-dydx-chain)

## A limit can restrict how far the order walks

A buy limit of 101 would not accept the 102 level. It could fill three units while leaving or cancelling the remainder according to its time-in-force rule. A market order prioritizes immediate matching but still depends on liquidity and venue-specific execution protections.

Evidence: [Perpetual order types on dYdX Chain](https://help.dydx.trade/en/articles/166981-perpetual-order-types-on-dydx-chain)

## Displayed depth can change

Orders can be filled or cancelled before another request reaches matching. A depth screenshot is a snapshot of quoted interest, not reserved inventory. Compare executed fills with the book’s timestamp, fees and order policy before concluding that a top-of-book quote was promised.

Evidence: [Interface of the Trade tab](https://help.dydx.trade/en/articles/166979-interface-of-the-trade-tab); [Perpetual order types on dYdX Chain](https://help.dydx.trade/en/articles/166981-perpetual-order-types-on-dydx-chain)

## Questions

### Is a narrow spread enough to show a market is liquid?

No. A tiny size can sit at the best prices while little depth exists behind it. Examine size across levels for the trade being considered.

Evidence: [Interface of the Trade tab](https://help.dydx.trade/en/articles/166979-interface-of-the-trade-tab); [Perpetual order types on dYdX Chain](https://help.dydx.trade/en/articles/166981-perpetual-order-types-on-dydx-chain)

## Claims and scope

### order-book-depth-spread-quick-answer

An order book lists bids to buy and asks to sell at specified prices and sizes. The spread is the gap between the best bid and best ask. Depth measures the quantity available across price levels; a trade larger than the best level can execute at several prices and have a worse average than the top quote.

Scope: {"collection":"defi","dataAsOf":"2026-10-02","blockHeight":null}

### order-book-depth-spread-fact-bid

Bid: A bid is a resting offer to buy.

Scope: {"collection":"defi","dataAsOf":"2026-10-02","blockHeight":null}

### order-book-depth-spread-fact-ask

Ask: An ask is a resting offer to sell.

Scope: {"collection":"defi","dataAsOf":"2026-10-02","blockHeight":null}

### order-book-depth-spread-fact-depth-chart

Depth chart: The chart aggregates orders by price level.

Scope: {"collection":"defi","dataAsOf":"2026-10-02","blockHeight":null}

## Sources

- [Interface of the Trade tab](https://help.dydx.trade/en/articles/166979-interface-of-the-trade-tab) — dYdX Operations Services. Definition and presentation of trading market metrics. Locator: Orderbook; Position information; Stats. Retrieved: 2026-10-02T18:53:20.712Z.
- [Perpetual order types on dYdX Chain](https://help.dydx.trade/en/articles/166981-perpetual-order-types-on-dydx-chain) — dYdX Operations Services. Order-type semantics and dYdX-specific constraints. Locator: Market; Limit; Stop; Take Profit; execution policies. Retrieved: 2026-10-02T18:53:20.714Z.

## Revision history

- 2026-10-02: First publication after primary-source research and separate automated verification.

## Cite this entry

Degrees of Satoshi editorial project. “Order-book depth and spread: reading the liquidity behind a quote.” Published 2026-10-02; updated 2026-10-02. https://degreesofsatoshi.com/encyclopedia/order-book-depth-spread/