Volume confirmation and its limits

In simple terms

Many chart methods use volume as a second opinion on price. The traditional rules, dating back to early chartists, say:

• During a pattern, such as a flag or triangle, volume tends to shrink as the market pauses.
• On a breakout, volume should expand, showing broad participation.
• Trends on rising volume are more trustworthy than trends on falling volume.

These rules describe common tendencies. This lesson looks at how to apply them consistently and how much they really add.

Measuring volume consistently

Raw volume cannot be compared between shares, or even for the same share over long periods. Use relative volume:

A breakout rule might then require relative volume above 1.5 or 2 on the breakout day. Writing the rule down, as the breakouts lesson recommends, makes the volume test objective.

Mechanical volume

Before reading volume as evidence of opinion, check for events that generate trading regardless of views:

• Index additions and removals: funds tracking the index must trade on a set date.
• Block and bulk deals: large negotiated trades between institutions, which the exchanges publish.
• Derivatives expiry: positions are closed or rolled over, raising volume in shares with futures and options.
• Corporate actions: splits and bonus issues change share counts, so volumes before and after need adjusting, as the adjusted prices lesson explains.
• Promotions in tip groups: sudden retail buying in small shares, often part of pump-and-dump schemes.
• Circular trading: volume manufactured among related accounts, as the market manipulation lesson describes.

What the evidence suggests

Studies of breakouts and patterns that include volume filters tend to find that requiring higher volume improves results somewhat in some markets and periods, and not at all in others. Even where it helps, many high-volume breakouts still fail, and fewer signals pass the filter. Volume makes a description richer; it does not turn a weak signal into a reliable one.

It is also worth remembering what volume can never show: every share bought was sold, so volume cannot reveal whether buyers outnumbered sellers, or who either side was.

Using volume sensibly

1. Use relative volume, with a written threshold.
2. Check for mechanical events before interpreting a spike.
3. Look at delivery percentage to see how much of the volume changed long-term ownership.
4. Treat volume as context, and test any volume rule on samples chosen in advance.

Why it matters

"Volume confirms price" is one of the most repeated phrases in chart analysis. Understanding how to measure volume properly, what distorts it and how modest its confirming power is helps you avoid over-trusting high-volume moves, especially those created by index changes, block deals or manipulation.

Limitations

Volume conventions vary between data sources, for example in how block deals are counted. Relative volume depends on the period chosen. Evidence on volume rules is mixed and sensitive to how tests are designed.

Common mistakes

• Reading volume as "buying pressure".
• Ignoring index changes, block deals and expiries.
• Using raw volume instead of relative volume.
• Assuming high-volume breakouts rarely fail.

Try it yourself

1. Find three breakouts in the past year on daily charts of shares you choose in advance.
2. Calculate relative volume and note the delivery percentage on each breakout day.
3. Check the exchange website for block deals, index changes or expiries on those days.
4. Record what happened over the next 20 sessions, and decide whether volume helped distinguish the outcomes.