Trading on a Centralized Crypto Exchange (CEX)
Most crypto traders and investors buy and sell digital assets on centralized exchanges (CEXs) like Binance, Coinbase, or Kraken.
Before you place your first trade on one of these platforms, there’s one crucial concept you need to understand: the order book.
What Is an Order Book?
An order book is a real-time list of all open buy and sell orders for a particular trading pair (like BTC/USD) on a crypto exchange. It gives you a “behind-the-scenes” view of current supply and demand in the market.
Every exchange has an order book for each trading pair it offers. For example:
- BTC/USD (Bitcoin to US dollar)
- ETH/USD (Ethereum to US dollar)
- ETH/BTC (Ethereum to Bitcoin)
- ADA/ETH (Cardano to Ethereum)
Each trading pair has its own independent order book.
How the Order Book Works
An order book displays all the pending or open limit orders placed by traders. These include:
- Buy orders (called “bids”)
- Sell orders (called “asks”)
As traders place, modify, or cancel their orders, the order book updates in real time.
For instance, the BTC/USD order book shows all current limit orders to buy or sell Bitcoin for U.S. dollars.
Since BTC is priced in USD in this pair, USD is the quote currency and BTC is the base currency.
Placing a Limit Order
Anyone can place a limit order, which is a request to buy or sell a crypto asset at a specific price.
That order will remain in the order book until:
- It gets filled (someone agrees to the price), or
- You cancel it manually.
Example:
You place a buy limit order to buy BTC at $30,000.
For your order to be filled, someone else must place a sell order at the same price.
But if another buyer places a higher bid (say $30,001), their order gets filled first. Why?
Because sellers want to sell at the best available price—which means they’ll accept $30,001 before $30,000.
Exchanges automatically prioritize the best price to protect users from accidentally accepting worse deals.
How to Use the Order Book
When you trade on an exchange, you have two options:
- Place a limit order
- This order stays in the book until another trader takes it.
- Take an existing order
- You accept a limit order that’s already in the book by placing a market order.
Understanding the Order Book Display
Here’s what a typical crypto order book looks like:
- Asks (Sell orders) – Shown in red
- Bids (Buy orders) – Shown in green
For each price level, you’ll see the quantity of crypto being offered to buy or sell.
This helps you visualize supply and demand:
- Sellers supply coins by placing sell orders.
- Buyers create demand with buy orders.
The Spread
The spread is the difference between:
- The highest bid (best price someone wants to buy at)
- The lowest ask (best price someone is willing to sell at)
Example:
- Best bid: $29,968.79 (buying 0.0474 BTC)
- Best ask: $29,969.62 (selling 0.0276 BTC)
- Spread = $0.83
A narrow spread usually means a more liquid market.
What If You Want to Buy?
You have two choices:
- Take the best ask (at $29,969.62)
- Use a market order to buy instantly at that price
- You’ll get 0.0276 BTC
- Place a buy limit order at your desired price
- For example, you might place a limit order at $29,950
- But unless a seller agrees to your price, your order will just sit in the book
Warning: If you place an unrealistic order (like buying BTC for $1), it will likely never get filled—unless the market completely crashes!
What If You Want to Sell?
If you already own BTC and want to sell, you also have two choices:
- Take the best bid (at $29,968.79)
- Use a market order to sell instantly
- You’ll sell 0.0474 BTC
- Place a sell limit order
- For example, you could set a limit price at $30,000
- Your order will wait for a buyer willing to pay that amount
Maker vs Taker Fees
Exchanges often charge different fees depending on how you trade:
- If you place a limit order, you’re a maker (you add liquidity)
- If you take an existing order, you’re a taker (you remove liquidity)
Taker fees are usually higher, so using limit orders can help reduce your trading costs.
Summary
The order book is a core part of any crypto exchange. It shows:
- The current buy and sell interest
- The price levels people are willing to trade at
- The quantity of crypto at each level
Knowing how to read and use the order book helps you:
- Make better trading decisions
- Time your trades
- Understand market dynamics