Who this is for — Anyone who needs to distinguish how much quantity was traded from how many transactions occurred and how much money changed hands.
Trading volume is the quantity of shares, contracts or units transferred during an interval. A transaction for a quantity of 100 increases volume by 100, not 200: buyer and seller are the two sides of the same transaction.
In plain terms — Volume states how much quantity was traded within the scope of the data. By itself, it does not reveal who had “more conviction”, who initiated the trade or where price will go.
Volume and nearby metrics
In plain terms — “Many trades” can mean many small transactions or a few large ones. Volume and trade count are not synonyms.
| Metric | What it counts |
|---|---|
| Volume | Quantity of units or contracts transferred |
| Trade count | Number of transactions |
| Turnover / traded value | Quantity × price, aggregated over the period |
| Open interest | Derivative contracts still open under the market's rules |
| Tick volume | Number of updates or ticks; a proxy, not traded volume |
Example — Ten transactions of 10 shares and one transaction of 100 shares both produce volume of 100, but their trade counts are 10 and 1 respectively.
An example you can recalculate
Teaching example: within the same one-minute bar on one venue, the feed reports three transactions in the same euro-denominated share. Each row is a separate execution, with no duplicates or corrections.
| Transaction | Shares | Price (€) | Traded value (€) |
|---|---|---|---|
| 1 | 40 | 100.00 | 4,000 |
| 2 | 10 | 101.00 | 1,010 |
| 3 | 50 | 100.40 | 5,020 |
Volume is 40 + 10 + 50 = 100 shares, trade count is 3, and traded value is 4,000 + 1,010 + 5,020 = €10,030. The quantity-weighted average price is €100.30, different from the last price of €100.40. Multiplying all volume by the last price would give €10,040 and would not reconstruct traded value.
For derivatives, distinguish traded value or premium from the notional exposure: price basis, multiplier and convention depend on the contract. For options, quantity × quoted premium × multiplier measures the premium traded, not the notional amount of the underlying. In crypto markets, distinguish base-asset quantity from value in the quote currency. A number without units cannot support a comparison.
The scope of the data
A volume figure can be interpreted only if the following are known:
- the instrument and, for futures, expiry or continuous series;
- a single venue or consolidated data;
- the session included and time zone;
- the bar interval;
- corrections, off-market trades, auctions and data-vendor rules.
Comparisons between bars with different scopes can be misleading. In futures, for example, the migration of liquidity from one expiry to the next changes individual-contract volume; in fragmented equity markets, a feed from one venue does not equal the whole market.
What volume does not reveal by itself
Every transaction has a buyer and a seller. Volume does not automatically identify:
- which side attacked liquidity;
- whether a position was opened or closed;
- whether activity was informed, hedging-related or mechanical;
- whether a price movement will continue or reverse.
Order flow describes order and execution flows according to the available data. The aggressor side may be supplied by the venue or estimated using a stated rule; volume alone does not reveal it. Bid/ask classification can be uncertain when quotes and trades are not synchronized. A volume bar’s colour may follow the price change without measuring buyer- and seller-initiated volume.
Common mistake — Reading “high volume” as bullish and “low volume” as bearish. Volume is an unsigned quantity: direction and meaning come from its relationship with price, liquidity, time and market structure.
Volume, open interest and liquidity
For one trade of one contract in an isolated example without expiries or adjustments, volume always rises by 1. If both sides open, open interest rises by 1; if both close, it falls by 1; if one opens and the other closes, it is unchanged. The aggregate change in open interest cannot classify each trade: openings and closings may offset.
Volume measures completed trades. Liquidity concerns execution conditions for a particular quantity and time: prices, depth and the ability to absorb orders. High volume in the previous bar does not promise sufficient depth for the next order.
Price and volume: an interpretive lens
In plain terms — Comparing activity with price movement can generate hypotheses; it does not assign a certain cause to a candlestick.
In Studies in Tape Reading (1910), chapter V, Wyckoff separates the last trade from current quotes and compares traded quantities with price movement. On pages 75–76 he offers a probable inference, explicitly uncertain because supply and demand change. The hypotheses below are editorial interpretations to check in context, not a deterministic law.
| Observation | Hypothesis to test | Alternative explanations |
|---|---|---|
| High volume, wide range | Participation and efficient movement | News, gap, thin liquidity |
| High volume, narrow range | Possible bilateral activity or absorption | Auction, market making, bar aggregation |
| Low volume | Less activity within the data scope | Time of day, holiday, roll, incomplete feed |
| Breakout with rising relative volume | Greater participation relative to the benchmark | Forced exits or an isolated event |
The benchmark should be consistent: the same time band, the same contract or roll rule and a stated historical window. A breakout on lower volume is not automatically false; it is one element to combine with price acceptance, follow-through and liquidity.
Volume records activity; it does not certify that buyer and seller are independent. Wash trading explains why economic control, risk, and account relationships must be tested before reading volume as genuine demand.
Summary card
- Unit: quantity transferred, counted once per transaction.
- It is not: trade count, notional value, open interest or direction.
- Before comparing: check venue, session, contract and interval.
Bronze Path — Module: What is a market?. Next: Volatility. Index: Bronze Path.
Sources
OCC/OIC — Options Basics, The Options Premium section — per-share premium and contract multiplier, distinct from exposure to the underlying.
CME Group — What Is Volume? — contract definition and counting; limits of inferring direction from volume.
Nasdaq — Volume — quantity of shares transferred.
CME Group — Volume and Open Interest Columns Explained — data scope and traded versus outstanding contracts.
HKEX — How to Read Open Interest Figures — July 2005, pp. 24–27, especially p. 26: openings, closings and transfers.
Richard D. Wyckoff — Studies in Tape Reading — 1910, chapter V, “Volumes and Their Significance”, pp. 75–76; last price versus quotes and uncertain inference.