Book imbalance

Book imbalance is calculated by comparing total resting size on the bid side against total resting size on the ask side, typically within a fixed number of price levels or a fixed distance from the current market price, then expressed as a ratio (bid size to ask size) or a percentage skew toward one side.

A heavily bid-skewed book, more resting size waiting to buy than to sell within the visible depth, is sometimes read as short-term bullish pressure: more buyers appear ready to defend price on a dip than sellers are ready to cap it on a rally. The reverse applies to an ask-heavy book. The read is strongest over very short windows, seconds to a couple of minutes, since resting orders can be added or pulled almost instantly and a snapshot imbalance can flip before it means anything.

Book imbalance is one of the easiest order-flow signals to game and one of the least reliable to trade on its own. Resting orders cost nothing to place and nothing to cancel, so a large one-sided imbalance can be created deliberately to influence perception, then pulled the moment it's tested, a pattern often called spoofing. Even when it's genuine, an imbalance says nothing about size waiting further back from the market that isn't visible in the displayed depth, or about aggressive market orders about to arrive that haven't shown up in the book at all. Treat it as a fast-decaying, easily manipulated input, never a standalone trade signal.

Bitcoin's order book at $114,000 shows 620 BTC resting on the bid side within twenty ticks of the market, against 240 BTC resting on the ask side over the same range, a roughly 2.6-to-1 bid-heavy imbalance. That skew holds for about ninety seconds before a burst of aggressive selling hits several of those bids, and within thirty seconds the imbalance flips to roughly even as the resting buy orders get consumed or pulled. The brief bullish read the imbalance offered didn't survive contact with real selling pressure, which is why it works better as a fleeting confirmation than a standalone signal. A trader who sized a position purely off that first reading, without watching whether it held under pressure, would have been positioned on a signal that was already gone.