Crypto order books and liquidity: depth, slippage and weekend gaps

A crypto order book is the live list of buy orders (bids) and sell orders (asks) waiting on an exchange at each price. Liquidity is how much you can trade near the current price without moving it: a deep book has large orders close to the mid price, while a thin book has small orders spread out. When you send a market order larger than the size at the best price, it fills against the next levels too, and your average price is worse than the quote. That difference is slippage, and it grows sharply when books are thin, such as at weekends, overnight and during fast markets.

Understanding the book explains a lot of crypto behaviour that otherwise looks random: why a coin can fall 10% in a minute and recover, why stop-losses fill far from their level, and why the same order costs more on a small exchange than a large one. The planned guide to how crypto exchanges work covers exchanges more broadly; this guide focuses on depth, slippage and timing.

What the order book shows

Picture two lists facing each other.

• Bids are buy orders, sorted from the highest price downwards. The highest bid is the best price at which you can sell immediately.
• Asks (or offers) are sell orders, sorted from the lowest price upwards. The lowest ask is the best price at which you can buy immediately.
• The spread is the gap between the best bid and the best ask. The midpoint between them is the mid price.

Each level shows a price and the total quantity resting there. Exchanges usually show the book as a ladder, and many also show a depth chart: two curves showing cumulative quantity as you move away from the mid price, bids on one side and asks on the other. A steep curve close to the middle means a deep book; a flat curve that only rises far from the middle means a thin one. The bid and ask guide explains quotes in forex terms; the logic is the same.

Makers and takers

Orders that rest in the book are called maker orders, because they make liquidity. Orders that execute immediately against the book are taker orders. Most exchanges charge takers a higher fee than makers, and some pay a small rebate to makers. A limit order that does not cross the spread is a maker order; a market order is always a taker order.

How a market order walks the book

A market order says: fill this quantity now, at whatever prices are available. If the best ask has enough quantity, you get that price. If not, the order consumes the best ask and moves on to the next one, and so on until it is filled.

Worked example: a 3 BTC market buy on a reasonably deep book

The book is illustrative. The asks are:

• 0.5 BTC at $50,000
• 0.8 BTC at $50,010
• 1.2 BTC at $50,025
• 1.5 BTC at $50,050
• 2.0 BTC at $50,100

You send a market order to buy 3 BTC. It fills:

1. 0.5 BTC at $50,000
2. 0.8 BTC at $50,010
3. 1.2 BTC at $50,025
4. The remaining 0.5 BTC at $50,050

The total cost is $150,063, an average of $50,021 per bitcoin. Against the quoted $50,000, that is $63 of slippage in total, about 4 basis points. On a liquid market, for this size, that is small.

The same order on a thin book

Now assume a quieter time with less resting liquidity. The asks are (illustrative):

• 0.2 BTC at $50,000
• 0.3 BTC at $50,040
• 0.4 BTC at $50,100
• 0.5 BTC at $50,180
• 0.6 BTC at $50,300
• 0.8 BTC at $50,450
• 1.0 BTC at $50,600

The same 3 BTC market order now takes everything up to $50,450 and 0.2 BTC at $50,600. The total cost is about $150,802, an average of about $50,267. Slippage is about $802, more than twelve times the first case, and the last fill is $600 above the quote. If that order was a stop-loss on a short position, the trader would have expected to exit at $50,000 and been filled on average more than half a percent worse.

The quote was the same in both cases. Only the depth changed. The slippage guide covers the concept across markets.

Measuring depth before you trade

Depth is normally quoted as the total value of orders within a certain distance of the mid price, for example "1% depth" or "2% depth" on each side. A market with $10 million of bids within 2% of the mid can absorb a $1 million sale with modest impact; a market with $200,000 cannot.

Practical ways to estimate your own impact:

• Look at the ladder for your size. Add up the quantity at each level until you reach your order size, and note the last price you would need. That is your rough worst fill.
• Compare your order with the top few levels. If your order is a small fraction of the quantity at the best price, slippage will usually be negligible in normal conditions.
• Watch how the book refills. On liquid markets, levels taken out by a large order are replaced quickly by market makers. On thin markets, the gap can stay open, and the next market order fills even worse.
• Check the spread through the day. A spread that widens sharply at certain hours is a sign that depth is thin then too.

For smaller coins, depth can be strikingly low compared with the market value of the coin. A token with a large market capitalisation can still have only a few hundred thousand dollars of orders near the mid on any one exchange, which is why prices of smaller tokens can move so violently. The planned guide to crypto market cap and dominance explains why market cap says little about how much can actually be traded.

Liquidity is fragmented across exchanges

Unlike a listed share with a main exchange, a cryptocurrency trades on many venues at once, each with its own order book. Prices on the larger exchanges stay close because arbitrage traders buy where it is cheap and sell where it is expensive, but each individual book is only part of the total liquidity.

This has three consequences:

• The same coin can be liquid on one exchange and thin on another. A large order on a small venue can move its price far from the global average, at least briefly.
• Different trading pairs have different depth. Bitcoin against a major stablecoin or the US dollar is usually deeper than bitcoin against a smaller fiat currency.
• A CFD price is built from these books. Crypto CFD brokers typically derive their price from one or more exchange feeds, or from liquidity providers, and add their own spread. When exchange books thin out, CFD spreads usually widen too. The crypto CFDs vs buying crypto guide explains how CFD pricing differs from trading on an exchange.

Why weekends and quiet hours are different

Crypto trades 24 hours a day, seven days a week, but liquidity does not stay constant. Much of the professional market-making activity, and the institutional flow, is concentrated in hours when traditional markets are open. At weekends, around public holidays and in the quietest overnight hours, books tend to be thinner and spreads wider.

Thin books matter in three ways:

1. Moves are larger for the same order flow. A sell order that would barely register on a Tuesday afternoon can push the price several percent on a Sunday morning.
2. Stops cluster and cascade. When a move takes out a group of stop-loss orders, each becomes a market order hitting the thin book, pushing the price into the next group. On derivatives exchanges, forced liquidations do the same.
3. CFD quoting may pause. Some brokers stop quoting crypto CFDs at weekends or during maintenance windows. When quoting resumes, the price may gap to where the exchanges have moved in the meantime. The planned guide to bitcoin trading hours and weekends and the gap risk guide explain the effect on open positions.

Flash crashes: what a thin book looks like under stress

A well-documented example came on 21 June 2017 on GDAX, the exchange then run by Coinbase. A single multimillion-dollar market sell order in ether pushed the price on that exchange from about $318 to about $224 as it walked down the book. That move triggered around 800 stop-loss orders and margin liquidations, which hit the remaining bids in turn, and the price briefly printed as low as $0.10 before recovering within minutes. The exchange said it found no wrongdoing, honoured the trades, and credited customers whose stops or margin calls had been triggered by the move.

The ether price on other exchanges barely moved. The crash was a property of one order book at one moment, not of the asset's value. Similar but smaller flash moves have happened many times since on individual venues and in individual pairs, especially in smaller coins.

The lesson for traders is practical. A stop-loss is a market order in waiting. In a thin book, it can be filled far beyond its trigger price, and when many stops sit at the same obvious level, they can feed each other. The crypto stop-loss placement guide (planned) covers where traders place stops and why obvious levels are risky; the order types guide explains stop-limit orders, which cap the fill price at the cost of possibly not filling at all.

Volume, wash trading and what to trust

Exchanges publish trading volume, and data sites rank coins and exchanges by it. Headline volume has a poor track record as a measure of real liquidity. In March 2019, asset manager Bitwise presented research to the US Securities and Exchange Commission arguing that about 95% of the bitcoin spot volume reported across the exchanges it examined appeared to be fake or non-economic, concentrated on unregulated venues. The industry and data providers have since tried to filter suspect volume, but wash trading (an entity trading with itself to inflate activity) and spoofing (placing large orders with no intention of letting them fill) remain known problems, particularly on less regulated exchanges and in smaller tokens.

What this means in practice:

• Prefer depth and spread over volume. A tight spread and real size near the mid are harder to fake for long than a volume figure.
• Treat sudden large orders on the book with caution. A large bid that vanishes as the price approaches it may never have been meant to fill.
• Be wary of tokens whose volume is concentrated on one obscure venue. If you cannot see deep, consistent books on established exchanges, the liquidity may not be there when you need it.

Practical habits for trading in thin markets

• Use limit orders where speed is not essential. A limit order lets you choose the worst price you will accept. You might not be filled, but you will not walk the book unexpectedly.
• Split large orders. Several smaller orders spaced out over time usually give a better average than one large market order on a thin book.
• Size for the slippage you could face. If a stop could realistically fill a few percent beyond its level at the weekend, include that in your risk calculation. The crypto position size calculator lets you test sizes against different stop distances.
• Check the book before trading smaller coins. If your order would consume several levels, the quoted price is not the price you will get.
• Be careful around weekends and holidays. Holding a leveraged crypto position through a thin period exposes it to larger moves, wider spreads and, on CFDs, possible gaps. The crypto volatility and risk guide covers why moves are so large.

Common mistakes

• Assuming the quoted price is the price for any size. It is only the price for the quantity at the top of the book.
• Using market orders in thin markets. On a quiet weekend or a small coin, a market order can fill far from the quote.
• Trusting headline volume. Volume can be inflated; depth and spread tell you more.
• Placing stops exactly at obvious round numbers or recent lows. Clusters of stops at the same level make cascades more likely.
• Ignoring fees on top of slippage. Taker fees, spreads and slippage add up, especially for frequent traders. The how to compare trading costs guide shows how to build an all-in cost.

Leveraged crypto trading carries a high risk of losing money. CFD providers' disclosures typically show between about 61% and 89% of retail accounts losing, and ESMA's 2018 analysis found 74% to 89%. Crypto prices can fall to a fraction of their value, and you can lose all of the money you put in.

Frequently asked questions

What is an order book in crypto?

It is the live list of buy and sell orders resting on an exchange at each price for a trading pair. The highest bid and the lowest ask set the current market, and the quantities behind them show how much can be traded at those prices.

What is market depth?

Market depth is the amount of buying and selling interest close to the current price, usually expressed as the total value of orders within 1% or 2% of the mid price. Greater depth means larger orders can be filled with less price impact.

Why did my crypto market order fill at a worse price?

Your order was probably larger than the quantity at the best price, so it filled against further levels in the book, or the book changed between your click and the execution. Both are slippage. It is more likely in thin markets, at weekends and in fast moves.

Is crypto less liquid at weekends?

Usually, yes. Crypto trades every day, but professional market makers and institutional flows are more active when traditional markets are open. Weekend books tend to be thinner and spreads wider, so similar orders can move prices further.

What causes a crypto flash crash?

Typically a large market order or a burst of forced selling hits a thin order book, the price falls through several levels, stop-losses and liquidations trigger, and those add more selling. Prices often recover quickly once the forced selling ends, as in the June 2017 ether flash crash on GDAX.

Is trading volume a good measure of liquidity?

Not on its own. Research presented to the SEC in 2019 argued that most reported bitcoin volume on the exchanges examined was not genuine, and wash trading remains a known issue. Spread and depth near the mid price are more reliable indicators of how much you can actually trade.