What does volume, trades and open interest mean?
Volume, trades, and open interest all measure how busy a market is, but they don't measure the same thing, and only open interest is actual money committed. Getting them mixed up is easy: a market can show a huge volume number and hold very little real money, or trade quietly while millions sit locked in open positions. Here's how each figure works in our dashboards, how they differ, and how to read them together, with a worked example at the end.
Volume
Volume on AllTop is notional volume: the number of contracts that changed hands, valued at each contract's $1 settlement price rather than what anyone paid. Kalshi's API reports the underlying field as "number of contracts bought on this market" — a plain count, with the dollar sign added at face value afterward, and both sides of every match included in the tally.
Because every contract counts at $1 regardless of its price, the volume figure is always larger than the money that actually moved, and the difference is biggest in low-priced markets. Volume is a good measure of how active a market is, but it isn't the amount traders spent.
Each venue cell on a row also carries its own volume figure, which is that venue's share of the activity. The split tells you where the liquidity actually sits — useful when you want a large order to fill without moving the price.
The 14D trend line
The sparkline plots a market's recent price history, showing whether its odds have been trending up or down. Every other column on the row measures how much traded; this one measures where the price went and how volatile the market is. The one-day version is the small percentage-point figure under the aggregated odds, showing the 24-hour move.
Spread
The spread measures the gap between venues' prices in percentage points. A small spread means the venues agree on the odds. A large one usually means they don't, though on a market with little or no trading, it can also reflect resting orders sitting far apart rather than real prices.
24H Trades and Markets Traded
The stat strip's trade count is the number of executions in the window. High volume across few trades points to large positions moving; thousands of small trades behind modest volume points to a crowd. Markets Traded counts how many distinct markets saw any activity at all, and it climbs on big news days as money spreads into markets that normally sit quiet.
Open Interest
Open interest is the figure that is literally dollars. Kalshi's API defines it as contracts bought "disconsidering netting" — the positions still open after offsetting trades cancel out — and every open contract is fully collateralized: the yes side posts the price, the no side posts the rest, and the exchange holds the combined $1 until resolution. Ten thousand contracts open means $10,000 committed and waiting on the outcome.
It's a snapshot, not a flow — never sum open interest across days. Monday's positions are mostly still there on Tuesday; adding the two figures counts the same locked dollars twice.
Volume and open interest together tell you what kind of activity you're looking at. Rising volume with rising open interest means new money is entering and staying. Rising volume while open interest goes flat or falls means positions are churning or closing out, which is common as a market heads toward resolution.
Reading a row: the tournament winner table
Spain shows $753K in 24-hour volume — roughly 753,000 contract-sides traded in a day. The per-venue cells split that into $35K on Kalshi and $717K on Polymarket at the same 59¢ price, so the liquidity lives almost entirely on one venue. The climbing sparkline says Spain's odds have risen over two weeks, and the 0.30pp spread says the venues agree.
Argentina's $1.5M is twice Spain's activity, and its falling trend line shows the odds cooling even as the money comes in.
The volume tracker
For the platform-wide picture, the volume tracker at /markets/volume/ publishes period totals, per-venue market share, category breakdowns, notable markets, and a 30-day daily history. The percentage change is calculated as the current minus the previous, divided by the previous.
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