How to Read a Crypto Order Book: Bids, Asks, Spread, Depth and Slippage (Beginner's Guide)
Every exchange screen has a column of red and green numbers that most beginners skip: the order book. It's worth learning to read, because it tells you what price you'll actually get, how much your order might move the market, and whether a pair is liquid enough to trade at all. This guide walks through bids and asks, the spread, depth, how market and limit orders interact with the book, why thin altcoin books cause slippage, and why big “walls” can mislead. It's educational only: no trading signals, no price predictions and no advice to buy or sell anything.
What an order book is
An order book is the live list of open orders for one trading pair, for example BTC/USDT. It has two sides. Bids are orders to buy: each line says “I'll buy this amount at this price or lower”. Asks (also called offers) are orders to sell: “I'll sell this amount at this price or higher”. Exchanges usually show asks in red above and bids in green below, with the most competitive prices closest to the middle.
Each row typically shows a price, an amount at that price, and often a running total. The highest bid and the lowest ask are called the best bid and best ask. A trade happens when someone is willing to meet the other side: a buyer accepts the best ask, or a seller accepts the best bid.
The spread: the first number to check
The spread is the gap between the best ask and the best bid. In other words, it's the difference between the highest price a buyer is currently willing to pay and the lowest price a seller is currently willing to accept. The SEC's investor education site has a short glossary entry on the bid-ask spread for stock markets; the same idea applies on crypto exchanges.
A narrow spread usually means many participants are quoting close prices, so you lose little by crossing it. A wide spread means that if you buy at the ask and immediately sell at the bid, you lose the gap. It's a hidden cost that never appears on the fee schedule. Comparing the spread to the price (as a percentage) is a quick way to compare pairs: a spread that's tiny on a major pair can be many times larger on a small altcoin.
Depth: how much is waiting at each price
The spread only tells you about the very best prices. Depth tells you how much volume sits behind them. If the best ask has only a small amount and the next rows are far higher, a modest buy order will “walk the book”: it fills the first row, then the next, then the next, each at a worse price. The average price you pay ends up above the price you saw.
Many exchanges also show a depth chart: two curves, bids on the left and asks on the right, rising as you move away from the middle. Steep, tall curves near the middle mean a deep book. Flat, low curves mean a thin one where even small orders move the price. Our explainer on altcoin liquidity on exchanges covers why depth varies so much between pairs.
How market and limit orders use the book
The SEC's page on types of orders describes the two basics, and they work the same way against a crypto book:
- A market order executes immediately but doesn't guarantee the price. It takes liquidity from the book, starting at the best ask (for a buy) or best bid (for a sell) and walking down the rows until it's filled.
- A limit order executes only at your price or better. If no one is willing to trade at that price yet, the order rests in the book and becomes one of the rows other people see. It may fill partly, fully or not at all.
On exchanges this is often described as takers (orders that fill immediately against the book) and makers (orders that rest in the book and add liquidity). Many exchanges charge different fees for each; check your exchange's own fee page rather than assuming.
Slippage, worked through without real prices
Imagine a pair where the best ask offers a small amount, the second row offers a bit more at a slightly higher price, and the third row is much higher. A market buy bigger than the first row fills partly at each level. The difference between the price you saw and the average price you paid is slippage. On a deep pair it's often negligible; on a thin pair it can be large. A limit order caps the worst price you'll accept, at the cost of possibly not filling.
Thin altcoin books: what to watch
- Gaps between rows. Big price jumps between consecutive levels mean any meaningful order moves the price.
- Small totals near the middle. Add up the amounts within a small range of the mid price and compare them with the size you have in mind.
- Wide spread that doesn't tighten. If the spread stays wide for hours, there are few active participants.
- Large recent trades that moved the price sharply. The trade history next to the book shows how prices reacted to past orders.
- Different books on different exchanges. The same coin can be liquid on one venue and very thin on another.
Why big walls can mislead
A “wall” is an unusually large order at one price level. It can look like strong support (a big bid) or a ceiling (a big ask). But an order in the book is only an intention until it's filled, and it can be cancelled in a second. Placing bids or offers with the intent to cancel them before execution is called spoofing; in the US it's prohibited on regulated futures markets under the Commodity Exchange Act, which describes it as “bidding or offering with the intent to cancel the bid or offer before execution” (7 U.S.C. § 6c(a)(5)(C)). Many crypto spot venues are less tightly supervised, so treat walls as information that can disappear, not as a promise.
Practical habits: watch whether a wall moves as price approaches it, compare the book with actual trades rather than resting orders, and don't size a position on the assumption that a wall will hold.
A five-step routine before placing an order
- Check the spread as a percentage of the price.
- Add up the depth within a small range of the mid price and compare it with your order size.
- Decide between market (certainty of fill) and limit (control of price).
- If using a market order on a thin pair, consider splitting it or using a limit instead.
- Confirm the pair, amount and order type on the confirmation screen before you submit.
Security belongs in the routine too: log in only from a bookmark and set an anti-phishing code, as described in our guide to exchange anti-phishing codes and bookmark logins.
Risk note
Reading an order book helps you understand execution costs. It does not predict where prices will go. Crypto assets are volatile, can lose most or all of their value, and exchanges can pause trading or withdrawals. Only trade amounts you can afford to lose, and consider independent, qualified advice for your situation.
If you are comparing app-based workflows instead of exchange order books, see our educational guide to CoinDrop versus Swappr (earn app or swap app) for which job each Android app fits.
FAQ
What do the red and green numbers mean?
On most exchanges, red rows are asks (sell orders) and green rows are bids (buy orders). Colours can vary by exchange and settings.
What is a good spread?
There's no universal number. Compare the spread as a percentage across pairs and venues; narrower generally means lower hidden cost.
Does a big buy wall mean the price will go up?
No. Orders can be cancelled at any time, and a wall says nothing certain about future prices.
Why did my market order fill at a worse price?
It probably walked the book: it filled across several price levels because the best level didn't have enough volume.
Sources
- Investor.gov (SEC): types of orders (checked 2026-10-10)
- Investor.gov (SEC): bid-ask spread (checked 2026-10-10)
- 7 U.S.C. § 6c, Cornell Legal Information Institute (checked 2026-10-10)
More guides: the CoinX blog.