Bid Ask Imbalance

Bid-ask imbalance refers to a meaningful disparity between the total volume of resting buy orders (bids) and resting sell orders (asks) visible in the order book at or near the current market price. When one side materially outweighs the other, it creates a temporary imbalance in passive liquidity.

How it is measured

At any moment, the DOM shows bid size and ask size at each price level. Summing the top N levels (e.g. the best 5 bids vs the best 5 asks) gives a snapshot of near-term passive liquidity:

Bid-Ask Ratio = Total Bid Size ÷ Total Ask Size

A ratio above 2:1 in favor of bids suggests more passive buyers than sellers near the current price.

Interpreting bid-ask imbalance

Heavy bids, thin asks: more passive buyers than sellers. Price may be pulled upward as the ask side is thinner and easier for aggressors to lift.

Heavy asks, thin bids: more passive sellers than buyers. Price may be pushed lower as the bid side offers less resistance to aggressive selling.

Balanced: neither side dominant. Price likely to chop until a catalyst creates directional flow.

The passive/aggressive relationship

Bid-ask imbalance measures passive intent. But passive orders do not move price: aggressors do. A heavy bid stack does not guarantee price goes up; it only means more buyers are willing to buy at current or lower prices.

The interaction between the imbalance (passive) and aggressive order flow (T&S, delta) gives the complete picture. Heavy bids + buy aggression in T&S = high-conviction long setup.

Limitations

Bid-ask imbalance is highly susceptible to manipulation. Algorithms routinely place, cancel, and modify orders faster than human perception. A visible bid-ask imbalance can vanish in milliseconds if it was placed to influence other participants rather than to genuinely trade. Use it as one input among several, not a standalone signal.