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How does a candle burn?

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Quick answer

Heat from a match melts and vaporises the wax near the wick. The wick draws liquid wax upward by capillary action, and the vapour reacts with oxygen, producing a flame. That flame's own heat melts more wax, so the candle keeps feeding itself until the wax runs out or the flame is extinguished.

A candle burns when heat melts and vaporises wax, and the wax vapour reacts with oxygen in a flame. The wick only delivers fuel; the visible flame is hot gas glowing as it combusts.

Step by step

  1. A match or lighter heats the wick until the wax around it melts into liquid.
  2. The liquid wax vaporises into a gas, because the flame's heat is far above wax's boiling point.
  3. Wax vapour rises and mixes with oxygen from the surrounding air.
  4. The mixture reacts, releasing heat, carbon dioxide and water vapour, and the hot gas glows as a flame.
  5. Heat from the flame melts more wax at the wick's base, which capillary action pulls upward to sustain the burn.

Key things to understand

  1. Lighting the wick raises its temperature until the wax coating melts and then vaporises into gas.
  2. Wax vapour mixes with oxygen in the air and reacts, releasing heat, carbon dioxide and water vapour.
  3. That heat melts more wax at the wick's base, which is drawn up the wick by capillary action to keep the flame fed.
  4. The bright zone is hot soot particles glowing; they finish burning in the blue outer zone where oxygen is plentiful.
  5. The flame settles at a steady size when heat produced by burning equals heat lost to the surroundings.

Labelled diagram

  1. Wick

    A braided cotton string that carries melted wax upward by capillary action.

  2. Wax pool

    Liquid wax at the wick's base, melted by heat radiating from the flame.

  3. Vaporisation

    The wick's heat turns liquid wax into combustible gas just below the flame.

  4. Mixing zone

    Wax vapour meets oxygen from the air and becomes ready to react.

  5. Flame

    Hot reacting gas glows; soot particles make the yellow upper zone.

  6. Heat feedback

    Flame heat melts more wax, closing the loop that keeps the candle burning.

How a candle flame feeds itself

Real-world examples

  • A birthday candle burns for a few minutes because its small wax reservoir is consumed quickly.
  • A church votive candle in a glass holder can burn for hours, since the glass blocks draughts and the wax pool feeds the wick steadily.
  • A candle in a sealed jar dims and dies once the trapped air's oxygen is used up, showing that combustion needs a constant oxygen supply.
  • A candle placed near a window flickers and smokes because moving air changes how fast wax vapour mixes with oxygen.

Common mistake

✗ Myth: The wick is what burns, and the wax is just there to hold it up.

✓ Fact: The wick is only a delivery system; the fuel is the wax vapour. Liquid wax is drawn up the wick, vaporises, and reacts with oxygen, while the wick itself chars slowly and is trimmed by the flame.

People also ask

What is a candle flame made of?
A candle flame is mostly hot gas: vaporised wax, oxygen, carbon dioxide, water vapour and nitrogen from the air. Tiny solid soot particles form inside it and glow yellow when heated. So the flame is not a solid object but a stream of reacting gases and glowing particles.
Why does a candle need a wick?
The wick acts like a pump and a wick, drawing liquid wax upward by capillary action to the hot zone where it can vaporise. Without it, a pool of wax would only burn at its surface and give a weak, uneven flame. The wick also holds the flame in place.
Does a candle burn wax or wick?
It burns wax vapour, not the wick. Heat melts and vaporises wax near the wick, and that gas reacts with oxygen to make the flame. The wick is consumed very slowly because the surrounding vapour burns before the cotton itself can fully catch.
Why does a candle flame flicker?
Flickering happens when moving air disturbs the flame. Small draughts, breathing or a fan push the hot gas sideways, changing how quickly vapour mixes with oxygen. The flame bends and dances to follow the airflow, which is why a candle in still air burns with a tall, steady tip.
Why is the bottom of a candle flame blue?
The blue zone sits where oxygen reaches the flame most easily, so the wax vapour burns completely and at a high temperature. Complete combustion produces little soot, and hot gas without glowing soot looks blue. The yellow part above is cooler and full of glowing soot particles.
Where does the wax go when a candle burns?
Most of the wax becomes invisible gases: carbon dioxide and water vapour that mix into the air. A small amount escapes as soot, the fine black smoke you see when a candle is blown out. Almost nothing solid is left behind, which is why a candle seems to disappear.
Why does blowing out a candle leave smoke?
Blowing removes the flame but the wick stays hot enough to keep vaporising wax for a moment. That vapour cools into tiny droplets and solid soot particles, forming the thin white trail of smoke. If you hold a match in that smoke, the flame can travel back down it to relight the wick.

Part of the guide: Everyday Science: Light, Heat & Matter →