Raw volume is directionless — it counts every trade equally. Delta goes further by splitting volume into aggressive buyers versus aggressive sellers. It measures market orders that lifted the offer (buys) minus market orders that hit the bid (sells) for each bar.
A positive delta bar means aggressive buyers dominated that period; a negative delta bar means aggressive sellers did. Shown as a histogram beneath price, it turns neutral volume into a directional order-flow reading of who was pressing hardest.
Reading delta with price
The most useful reads come from comparing delta with price. When price rises and delta is strongly positive, buyers are genuinely driving the move. When price rises but delta is weak or negative, the rally is being quietly sold into — a divergence worth noting.
- Delta = aggressive buy volume minus aggressive sell volume per bar.
- Positive delta = aggressive buyers dominated; negative = sellers dominated.
- Delta agreeing with price supports the move.
- Delta diverging from price warns the move may lack real backing.
An important honest limit: true delta needs tick-level bid/ask data from a real exchange feed, so it is reliable on futures and stocks but often unavailable or estimated on CFDs and forex. Know what your platform is actually calculating before you trust it.
Delta reveals who was aggressive — buyers or sellers — and its divergence from price is one of order flow's most telling clues.