what does 'BS' and 'AS' stand for in TOS

June 26, 2026

In TOS, BS usually means bid size and AS means ask size. They show how much size is sitting on each side of the market at a given price level.

What they mean

BS = Bid Size : the number of shares/contracts currently bidding.
AS = Ask Size : the number of shares/contracts currently offered for sale.
In Level II or order-book style displays, these values help show market depth and queue size.

Why it matters

A larger bid size can suggest stronger buying interest.
A larger ask size can suggest stronger selling pressure.
The numbers can change quickly, so they’re best read as a snapshot, not a guarantee of direction.

Simple example

If you see BS 500 and AS 800 , that means there are 500 units on the bid side and 800 on the ask side at that moment.

TL;DR: In TOS, BS = bid size and AS = ask size.