Spread and Mid Price
Two of the most common reference values in an order book UI are the **spread** and the **mid price**.
Spread
The spread is:
text
best ask - best bidExample:
| Best Bid | Best Ask | Spread |
|---|---|---|
| 171.98 | 172.02 | 0.04 |
The spread gives a quick sense of how tight or wide the market is.
Mid price
The mid price is the midpoint between best bid and best ask:
text
(best bid + best ask) / 2It is a reference value, not necessarily an executable trade price.
Why the spread matters
The spread often reflects:
- liquidity conditions
- market maker activity
- short-term uncertainty
- how easy it is to cross the market without paying a large penalty
Why the mid matters
The mid is useful for:
- centering a depth view
- comparing nearby price levels
- measuring relative movement around the touch
UI note
The mid should usually be visible, but it should not dominate the ladder.
It is a reference line, not the main data surface.