How to Read Volume Bars Under a Stock Chart

Volume 4.2M. Avg volume 1.4M. Those two fields sit next to each other on most quote pages, and the bars under the price chart are the same data drawn day by day. Today’s bar is three times the height of a normal one. The job is to work out whether that tells you anything.

Know what a bar counts

Each bar is the number of shares that changed hands during one period of the chart. On a daily chart that’s one session. On a five-minute chart, it’s five minutes. Every trade counts once, whether it was a buyer lifting the offer or a seller hitting the bid, so a bar measures activity with no direction built in.

The color adds the direction. Most charts shade a bar green or up when the period closed higher and red or down when it closed lower. Tools differ on the comparison, though. Some color against the previous period’s close, others against the same period’s open, and on a day that gaps up and then fades the two methods give opposite colors. Check your chart’s settings once so you know which one you’re looking at.

Premarket and after-hours trades may or may not be included in the daily bar. That depends on the platform too.

Compare each bar with the average line

A bar on its own has no scale. A stock that trades 20 million shares a day and one that trades 200,000 both draw bars that fill the panel once the axis rescales to fit, so the only reading that means anything is each bar measured against that particular stock’s own normal day.

Turn on the average-volume line. It is usually a moving average of the bars over the last 20 or 50 periods, and the length is a setting you can change. Bars well above the line are unusual days. Bars under it are quiet ones.

That ratio is what screeners call relative volume. The case for leaning on it over raw share counts is made in relative volume says more than volume.

Watch volume at breakouts and pullbacks

Price clearing a resistance level or a trendline is where volume earns its place on the chart. A break on a bar well above average means a lot of participants traded through that level and accepted the new price. A break on a bar below average means very few did. The low-volume version can hold. It fails more easily, because there is less commitment behind it and fewer buyers who now have a cost basis to defend.

Then watch the pullback. After a breakout, prices often drift back toward the level they just cleared, and light bars on that drift suggest sellers are not showing up in size, while heavy red bars on the retreat say the move is being sold hard by people who were waiting for a chance to get out.

Each of these readings has exceptions. Use them as context for the price action.

Explain every spike

Big bars have causes, and most of them are on the calendar. Earnings releases produce the tallest bars most stocks print all year. News does the same: a guidance change, an 8-K, an analyst downgrade.

Some spikes have nothing to do with the company:

• Index changes. When a stock is added to or dropped from a widely followed index, funds that track it trade on the effective date, often right at the close, and the bar reflects their rebalancing.
• Options expiration. Monthly expirations can bring heavy trading as positions are closed, rolled or hedged.
• Quarter-end and rebalancing days across the market.

These bars are real volume from real trades, yet they say little about how investors feel about the business, so before you read a spike as conviction, check whether the calendar already explains it.

Read intraday bars against the day’s shape

Trading in US stocks is heaviest near the open and the close, with a lull through the middle of the session. Plotted on a five-minute chart, the bars form a rough U. So a tall bar at 9:35 a.m. is normal and a tall bar at 1 p.m. is not.

That shape also distorts early-day numbers. If you straight-line a partial day into a full-day estimate, the heavy open makes the projection too high.

Better tools compare today’s volume with the average volume by the same time of day. If yours does, use that figure; if it only offers a full-day average, discount the morning reading.

What trips people up

The biggest error is treating volume as direction. A huge red bar says many shares traded on a down day; it does not tell you who started it or whether the selling is finished. Another is comparing bars across stocks, since share counts depend on share price and the size of the company. A third is forgetting liquidity. A stock that averages very few shares a day will show wild relative-volume readings from a single large order, which is why setting liquidity minimums first keeps those names out of a scan before they can mislead you.