What Is Liquidity in Crypto? Order Book Depth Explained
Liquidity is how easily you can trade a crypto asset without moving its price. Learn how order book depth, top-of-book size and spreads measure it.
Updated
Liquidity is how easily you can buy or sell an asset quickly without moving its price. In a liquid market, large orders fill close to the quoted price and the bid-ask spread is tight. In an illiquid market, even modest orders push the price and cost you through slippage.
Key takeaways
- Liquidity is about how much you can trade now, at what cost.
- On order books, it is measured by spread, top-of-book size and depth.
- Top-of-book size is the most you can fill at the quoted best price.
- Depth within ±1% or ±2% of mid shows how much size sits near the current price.
- Volume is not liquidity: it measures past trading, not available orders.
- In arbitrage, the thinner book limits your size.
Where liquidity comes from
On a centralized exchange, liquidity is the set of resting limit orders in the order book. Much of it is posted by market makers, firms or traders who quote both a bid and an ask and earn the spread. Retail limit orders add to it as well.
On an AMM-based decentralized exchange, liquidity is the tokens deposited in a pool by liquidity providers. The larger the pool, the less each trade moves the price. See CEX vs DEX for how the two models differ.
Liquidity is not fixed. Market makers can cancel orders in milliseconds, so a book that looks deep can thin out quickly during a sharp move.
The three measures of order book liquidity
1. Spread
The gap between the best bid and best ask, usually shown in percent. It is the cost of the first unit you trade.
2. Top-of-book size
The quantity resting at the best bid and at the best ask. If the best ask is $100.00 with 400 units, you can buy up to 400 units at $100.00. Unit 401 costs more.
3. Depth
The total size at all price levels within a range of the mid price. A common metric is 2% depth: the dollar value of bids within 2% below mid and asks within 2% above. It answers the question: how much can I trade before the price moves 2% against me?
Worked example: top of book vs depth
Assume two exchanges quote the same token with the same spread.
| Ask level | Exchange A size | Exchange B size |
|---|---|---|
| $100.00 (best ask) | 400 | 5,000 |
| $100.20 | 600 | 6,000 |
| $100.50 | 1,000 | 8,000 |
| $101.00 | 3,000 | 10,000 |
You want to buy 2,000 units.
On Exchange A:
- 400 × $100.00 = $40,000
- 600 × $100.20 = $60,120
- 1,000 × $100.50 = $100,500
- Total: $200,620, average price $100.31, slippage 0.31%
On Exchange B:
- 2,000 × $100.00 = $200,000, average price $100.00, slippage 0%
Both exchanges show the same price and spread on a ticker. Only the depth reveals that the order costs $620 more on Exchange A.
Liquidity vs trading volume
Trading volume and liquidity are related but not the same.
| Trading volume | Liquidity | |
|---|---|---|
| What it measures | Amount traded over a period | Amount you can trade now without moving price |
| Time frame | Past (for example, 24 hours) | Present |
| Where to see it | Tickers, market data sites | Order book, depth charts, pool size |
| Can it be misleading? | Yes, volume can be inflated or concentrated in bursts | Yes, orders can be cancelled instantly |
Active markets usually attract market makers, so high volume and high liquidity often go together. But a token can trade heavily for a day on news while its book stays thin. Always check depth before sizing a trade.
Liquidity in derivatives markets
Perpetual futures have their own order books, separate from spot. A coin can have a deep spot market and a thin perp market on the same exchange, or the reverse. For perps, traders also watch open interest, the total size of outstanding contracts, as a sign of how active a market is. Open interest is not the same as order book liquidity, but very low open interest often comes with thin books.
Why liquidity matters for arbitrage
An arbitrage trade buys on one venue and sells on another. Two liquidity limits apply:
- The smaller top-of-book size sets the size at the quoted edge. If Exchange A offers 0.4 BTC at its best ask and Exchange B bids for 1.2 BTC at its best bid, only 0.4 BTC can be traded at the displayed spread.
- Beyond that, each extra unit eats into the edge. Walking up A's asks and down B's bids narrows the gap level by level until it disappears.
Example with assumed numbers: a 0.30% edge at the top of book might shrink to 0.10% at three times the top-of-book size and to zero at five times. After taker fees on both legs, the profitable size may be only a fraction of what you planned.
Liquidity also matters on exit. A funding rate position you open in a calm market must be closed later, possibly when books are thinner.
Common mistakes
- Sizing from the ticker price. The ticker shows one price; your order fills across many.
- Trusting a snapshot. Depth can vanish within seconds when volatility rises.
- Confusing volume with depth. High 24-hour volume does not guarantee a deep book right now.
- Ignoring the thinner leg. In a two-leg trade, the weaker book decides your cost.
How ArbTide helps
The arbitrage scanner shows the size available at the top of both books for each route, so you can see how much of a spread is actually executable. For funding trades, compare venues on the funding rates page and check each market's depth before sizing.
Frequently asked questions
- What is liquidity in crypto?
- Liquidity is how easily an asset can be bought or sold quickly without significantly changing its price. A liquid market has tight spreads and plenty of size at each price level.
- What is order book depth?
- Order book depth is the total size of buy and sell orders resting at different price levels. It is often measured as the value of orders within a set distance from the mid price, such as 1% or 2%.
- What is top-of-book size?
- Top-of-book size is the quantity available at the best bid and the best ask. It is the largest order you can fill at the quoted price without moving into worse price levels.
- Is trading volume the same as liquidity?
- No. Volume measures how much traded over a period, while liquidity measures how much you could trade right now without moving the price. A market can show high volume and still have a thin order book.
- Why does liquidity matter for arbitrage?
- The executable size of an arbitrage trade is limited by the thinner side of the two books. A price gap that exists only for a tiny amount of size cannot be captured profitably at scale.