Instruments · What it actually measures

Reading Volume

The only common series on a chart that is not a transformation of price — which makes it the only one that can contain information price does not already have. It is also the one most people read backwards, because it does not measure pressure. It measures how many people changed their minds.

Four exhibitsOne correctionInstruments series

Companion to the pattern series — ascending triangle, ascending channel, rising wedge, falling wedge — where volume does most of the confirming work.

There is no such thing as buying volume

This has to come first, because almost every popular description of volume is built on a mistake that a single sentence removes.

Every share that was sold was bought. Every contract that was opened was opened by two people taking opposite sides. Volume counts transactions, and a transaction has a buyer and a seller in exactly equal measure, always.

So "heavy buying volume" is not a thing that can exist. A day with ten million shares traded is a day on which ten million shares were bought and ten million shares were sold. Volume cannot be bullish or bearish on its own, and any reading that treats it as a force pushing price in a direction is describing something that is not there.

Volume does not measure pressure. It measures how much inventory changed hands — how many people, at that price, decided they were on the wrong side.

What it does tell you

Three things, none of which is direction:

How much ownership changed. High volume means a large share of the float found new owners at these prices. Low volume means the same people still hold it and price moved anyway.
Whether anyone new turned up. A move on expanding volume brought participants who were not there before. A move on contracting volume is the existing population re-pricing itself, which is a much weaker thing.
How hard price had to work. Volume set against the range it produced is the single most useful derived reading on the chart, and it is what section 04 is about.

Everything useful in the rest of this page comes from combining volume with something else. On its own it is a number with no sign.

Four combinations, four meanings

Volume acquires a sign only when you pair it with what price did. There are four pairings and they mean genuinely different things.

Exhibit 1 · The pairing mapPrice direction × volume level

Read it by column, not by cell. The left column is participation — the move is being paid for and ownership genuinely changes. The right column is an absence of resistance: the same holders re-pricing each other with nobody new arriving. Neither column is a signal on its own; both change what an otherwise identical candle means.

Expansion with the move

New participants arriving. Ownership is genuinely changing at these prices, which is what makes a level or a breakout durable — the population that would have sold it back has been replaced.

Contraction against the move

No new money. Price is travelling through a thin book because nobody is standing in the way, not because anybody wants it. These moves retrace easily, because nothing was actually transferred.

Six episodes on one chart

The same instrument through six volume regimes, which is more instructive than six separate examples because the price action alone would not distinguish them.

Exhibit 2 · Volume regimes in sequencePrice · Volume · Annotated

Two of these advances look almost identical in price and mean opposite things. The first is bought; the second is drift on fading participation and gives everything back. The climax bar is the largest volume on the chart and marks the high, not a continuation. The absorption zone at the lows is heavy volume producing almost no range — the most valuable single read on the page.

Absolute volume is almost meaningless

Ten million shares is a big number for one instrument and a quiet afternoon for another. Even within one instrument it means different things in different weeks. The raw number is not comparable to anything, including its own past.

The fix is to express every bar as a ratio to its own recent average — twenty periods is the conventional window and the exact choice matters much less than doing it at all. That single transformation is what turns volume from a decorative panel into an instrument.

Exhibit 3 · Raw volume vs. relative volumeSame bars, two readings

The top panel is what the chart shows by default. The bottom is each bar divided by its own twenty-bar average, with the 1.0 line marked. Bars that look unremarkable in the raw panel cross 2× in the relative one, and the tall bars in the middle of the raw panel turn out to be ordinary for that stretch. The relative reading is the one that carries information; the raw one mostly tells you what time of year it is.

Two corrections worth making beyond that

Time of day, if you trade intraday. Volume follows a pronounced U through a session — heavy at the open, thin at lunch, heavy into the close. A bar at 12:30 with the same volume as a bar at 09:45 is a far more unusual event. Compare each bar to the same time of day, not to the session average.
Scheduled events. Earnings, index rebalances, option expiries and futures rolls produce volume that has nothing to do with anyone's opinion of price. Treating a rebalance print as conviction is one of the more common ways to misread a chart badly.

Effort against result

The most useful thing you can do with volume is divide it by the range it produced. That ratio is the closest thing on a chart to a measure of resistance — in the physical sense, not the trendline one.

A bar that trades enormous volume and closes where it opened has done a great deal of work and got nowhere. Something absorbed all of it. A bar that trades almost nothing and moves three percent has met no resistance at all — which sounds bullish and usually means the book was simply empty.

Exhibit 4 · Volume per unit of rangeWhere the work went

Each bar's volume divided by its own high-to-low range, indexed to the chart's median. The spikes are absorption — heavy participation producing no movement, which means a large passive participant was taking the other side of everything. Those bars cluster at the lows here, several sessions before price turned, and they are invisible in both the price panel and the raw volume panel.

High volume, small range, at lows

Absorption. Someone large is buying everything offered without letting price rise, because moving it up would spoil their own fill. Bullish, and it looks like nothing happening.

High volume, small range, at highs

Distribution. The same mechanism with the signs flipped — supply meeting every bid without letting price fall. This is what a top looks like from the inside, and it is uneventful.

Both of those are the same measurement. Which one you are looking at is decided by where it happens in the structure, not by the reading itself — the recurring theme of this whole series.

What volume cannot do

It is not comparable across venues. In fragmented markets — equities especially — your feed may show one exchange's prints, or consolidated tape, or something in between. Off-exchange and dark volume may be reported late or not at all. The number you see is a sample, not the total.
Spot crypto volume is partly fictional. Exchange-reported figures have a long history of inflation, and wash trading is not rare. Prefer venues with credible reporting, or use futures volume and open interest instead.
It is a confirming instrument, never a leading one. Volume tells you what a move was made of after the move exists. Every reading on this page requires price structure to interpret it — which is why the same dry-up is bullish in a triangle and bearish in a rising wedge.
Tick volume is not volume. On instruments that report no real size — much of spot FX — most platforms substitute the number of price changes. It correlates with activity and is not the same measurement; treat conclusions drawn from it as weaker.

Using it

Put a 20-period average on the volume panel and read every bar against it. If you change one thing after reading this page, that is the one.
Never read volume without price structure. The number has no sign until you pair it with what price did and where in a structure it happened.
Expansion should agree with the move you believe in. Breakouts, breakdowns and reversals all want participation. Without it you are looking at drift through an empty book.
Watch for persistence, not one bar. A single heavy bar is a probe or an event print. Several consecutive heavy bars are a change of ownership, and only the second one is durable.
Treat the largest bar on the chart with suspicion. Climax volume marks ends far more often than beginnings — it is what maximum participation looks like, and maximum participation means the marginal participant has arrived.
Learn to see heavy volume with no range. It is the least dramatic thing on a chart and the most informative, because it is the signature of somebody large who does not want to move the price they are trading at.

A description of market mechanics, not trading advice.