Price tells you what happened. Volume tells you how many people were involved.
That second number is not a signal on its own, and treating it as one is the usual mistake. What it does is grade the reliability of everything else on the chart.
What volume is not
It is not directional. High volume on a green candle and high volume on a red candle are the same fact — lots of trading. Volume has no sign.
It is not open interest. Volume counts contracts traded during the session. Open interest counts positions still standing. A day can have enormous volume and no change in OI at all, which means people were trading with each other and going home flat.
It is not a leading indicator. Volume describes participation in a move that is already happening.
The one question it answers
Does this move have real participation behind it, or did it happen because nobody was there?
A 200-point move on the year's thinnest volume and a 200-point move on the year's heaviest are different events with the same price outcome. The first happened in a vacuum. The second required actual capital to change hands.
The four combinations
| Price | Volume | Reading |
|---|---|---|
| Rising | Rising | Healthy advance — buying with conviction |
| Rising | Falling | Advance running out of participants |
| Falling | Rising | Genuine distribution or panic |
| Falling | Falling | Drift lower, not active selling |
The second row is the useful one. A rally on steadily declining volume is a rally nobody is joining. It can continue for a while — thin markets drift upward easily — but there is no fresh capital supporting it, and it tends to reverse quickly when tested.
Volume at levels
This is where volume earns its place, because it makes the support-and-resistance mechanism observable.
A breakout on heavy volume means the level was cleared by real participation. Many people took positions on the other side of it.
A breakout on thin volume means price slipped through when few were watching. These fail far more often — the level was not overcome, it was merely stepped over.
A test that holds on heavy volume is a strong signal. Sellers pushed hard, buyers absorbed it, and the level held with real capital defending it.
Volume in Indian derivatives
Two important adjustments for F&O.
Index options volume concentrates near the money and at round strikes. Far strikes can show almost no volume, which is a tradability warning as much as a sentiment one — you can enter and struggle to exit.
Expiry days distort everything. Volume spikes enormously as positions are closed and rolled. Comparing expiry-day volume to a normal Tuesday tells you nothing.
Compare volume to the same instrument's recent average, and be careful comparing across expiries.
The limits, honestly
Volume is unreliable intraday at the extremes. The opening and closing auctions produce spikes that reflect mechanics rather than conviction.
Averages shift with regime. "High volume" means high relative to the last twenty sessions, not to some absolute figure.
It confirms, it does not predict. Every genuinely useful volume reading is about a move that has already begun. It improves your confidence in a signal; it does not generate one.
If you find yourself building a strategy where volume is the entry trigger, you have almost certainly reversed the relationship.
Check yourself
0 of 4 answered1.Nifty rallies 200 points on volume well below its 20-day average. What does this suggest?
2.What is the difference between volume and open interest?
3.Price breaks a well-watched resistance level on unusually thin volume. What is the sensible reading?
4.Why is comparing expiry-day volume to a normal session misleading?
What to take away
- Volume measures participation, not direction. It has no sign.
- It grades a move; it does not generate one. Read price first.
- Rising price on falling volume is a rally nobody is joining.
- At levels: heavy volume breaks hold, thin volume breaks get retested.
- Volume ≠ open interest. Activity is not commitment.
- Compare to the instrument's own recent average, and treat expiry days separately.