Open interest counts the number of perpetual contracts currently open on a market. Every long is matched by a short somewhere in that count, so the raw number says nothing on its own about which direction traders are positioned. Reading it correctly means pairing it with what price is doing at the same time; on its own, the raw figure explains very little. Understanding what it is not measuring is as important as understanding what it is.
Open interest is a snapshot of outstanding, not-yet-closed contracts at a point in time. Volume is a flow: the total notional or number of contracts traded over a period, such as an hour or a day. A single contract can change hands many times within a day, adding to volume on every trade, while adding to open interest only once and staying there until it is closed. High volume alongside flat open interest means positions are simply changing hands; rising open interest means new positions are being opened, net of whatever is being closed at the same time. A market can show enormous daily volume while its open interest barely moves, which simply means the same pool of positions is being actively traded back and forth.
The two metrics answer different practical questions. Volume is a reasonable proxy for how easily a large order can be worked through the market over time, since it reflects how much genuine trading activity is passing through. Open interest is a better proxy for how much leveraged exposure currently sits on the market waiting to be closed, one way or another, and the two can diverge sharply: a market can have thin daily volume but a large legacy open interest built up over a longer period, which behaves very differently under stress than a market where both figures are small.
Open interest increases when a new long and a new short are opened against each other. It stays flat when an existing position simply changes hands to a new counterparty. It decreases when a long and a short holder close out against each other, or when a position is liquidated and closed. Because every open contract needs both a long and a short side, open interest can never by itself reveal the ratio of longs to shorts, only how many matched pairs currently exist.
A market that has built up a large amount of open interest, particularly leveraged open interest concentrated near current price, carries more forced selling or buying pressure sitting just below or above the market than a market with little open interest. If price moves far enough to start triggering liquidations, those forced closes can push price further in the same direction, triggering the next band of liquidations in turn. This cascading pattern is a well-documented feature of leveraged derivatives markets generally, and it is one reason a market with heavily built-up open interest can move faster once a trend starts than the underlying spot demand alone would suggest.
The same dynamic runs in reverse as a stabilizing force once the cascade has cleared: heavy liquidations remove exactly the overleveraged positions that were most vulnerable to being forced out, which is why open interest often falls sharply right after a large, fast move and the market frequently finds it easier to stabilize once that flush has happened, since the remaining open interest is, by construction, the positions that survived the move.
This is a standard heuristic for reading positioning, useful as a starting read but never a guaranteed signal; open interest and price can also move together for reasons unrelated to conviction, such as a new market simply attracting its first liquidity after listing, which shows up as rising open interest regardless of any directional trend in price.
Open interest is measured per venue, and a figure that adds up open interest across many venues is not automatically the same as netting long and short exposure across a trader base. A market maker or an arbitrage desk running a long position on one venue against a short position on another shows up as open interest on both, even though the two positions largely offset each other from that trader's own perspective. Aggregated open interest is a useful gauge of overall market activity, but it should not be read as a clean measure of net directional exposure across the whole market. Where a position built on that open interest is actually marked, and how it gets liquidated, is covered in mark price versus index price ; how the position itself is structured is covered in perp position types .
Open interest is related to, but distinct from, order-book depth. Depth describes how much size sits on the book at a given distance from the current price, and it governs how far a single order will move that price right now. A market can carry large open interest built up over time while still showing thin order-book depth at this exact moment, and the two should not be treated as the same thing when sizing a trade.
Open interest in crypto perpetuals is the total number of contracts currently open on a market, counting every matched long-and-short pair once. It rises when new positions are opened, falls when positions are closed or liquidated, and stays flat when an existing position simply changes hands to a new counterparty.
Market depth is the amount of resting order size available at each price level away from the current price on an order book. It determines how far a single order of a given size will move the price, and it is a separate measure from open interest, which reflects outstanding positions.
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