What is an order book?

All types of exchanges, whether it be a stock, bond or cryptocurrency exchange need a way of displaying all of the outstanding orders for each instrument being traded. This is done using an order book. An order book is a digital, real-time, constantly updating list of all the outstanding buy and sell orders for an instrument, organised by price.

The BitMEX order book

The order book is organised in rows and split into two halves. Each row contains price levels and the number of contracts for each corresponding price. The “Total” column shows a cumulative count of contracts from the middle of the order book to each price level.

The top half of the order book contains sell orders (in red) often referred to as “asks”, the bottom half contains all buy orders (in green) often referred to as “bids”. All orders displayed in the order book are limit orders.

As seen in the image below, the best bid is the highest price someone is willing to pay for XBTUSD, which is 10,350 - this is shown at the top of the bids section (in green). The best ask is the lowest price someone is willing to sell XBTUSD at, in this case, 10,350.5. This can be seen at the bottom of the asks section of the order book (in red). The difference between the best bid and ask is known as the “spread”.

The middle of the order book

Between the buys and sells in the order book, there is also additional information that is useful to traders. 

  1. This shows the last price of the instrument. This is the price traders will see on the trading chart. 

  2. This shows Index Price / Mark Price of the instrument. The index is the .BXBT price. 

  3. These five lights show your position in the deleveraging queue. If all five are lit up, in the event of a liquidation your positions may be reduced.

How to customise your order book

You can customise the order book based on your needs and preferences. Click the settings icon in the top right corner of the order book. Here you have options to change the number of columns, the grouping and whether you want alerts on liquidations.

Switching to a two-column view puts bids and asks side by side rather than on top of each other. In this view, the last price, index price, mark price and deleverage queue are all shown on the top row.

Adjusting the order book grouping changes the size of the intervals between prices for a more clear view of where orders are currently placed.