Candle Melt Pool Diameter Calculator

The melt pool is the circular area of liquefied wax that forms when a candle burns.
A proper melt pool should reach the full diameter of the container within 1–2 hours of burning. If the melt pool is too small, the candle “tunnels”, wasting wax along the walls. If it is too large or too deep, the candle may overheat, smoke, or become a fire hazard.

Melt Pool Rule

The ideal melt pool reaches edge to edge within the first burn (1–2 hours) and should be 6–13 mm (¼–½ inch) deep. The primary factor controlling melt pool diameter is wick size relative to container diameter.

Wick Heat Output Estimation

Different wick series have known melt pool diameters. A simplified model:

Expected Melt Pool Diameter = Wick Throw Diameter × Wax Factor

Where:

• Wick Throw Diameter is the rated melt pool size for the wick series and size number
• Wax Factor adjusts for wax type: Soy = 0.85, Paraffin = 1.0, Coconut blend = 0.90, Beeswax = 0.80, Palm = 0.95

Wick Series Reference (Approximate Melt Pool Diameters)

Worked Example

A container with 8 cm diameter, using a medium ECO wick in soy wax:

Expected melt pool = 7.0 × 0.85 = 5.95, which the calculator rounds to one decimal and reports as 6.0 cm.

That is 75% coverage, leaving 2 cm of unmelted wax across the container, so 1 cm of hard wax standing on each side. The wick is too small. Size up to a large ECO wick and you get 8.5 × 0.85 = 7.2 cm, which is 90% of the container and much closer to the edge.

Multi-Wick Candles

For containers wider than 10 cm (4 inches), a single wick often cannot achieve a full melt pool. Use multiple wicks spaced evenly. Each wick contributes its own melt pool, and where pools overlap they merge.

Merged pools do not simply add up, which is why the calculator applies a factor here:

Combined pool = Single pool × Number of wicks × 0.6

Two wicks therefore buy about 1.2 times the reach of one, not double it, and three buy about 1.8 times. The result is capped at the container diameter, since a melt pool cannot be wider than the jar it is in. Space wicks 5–7 cm apart for optimal coverage.

A wick can also be too big. If the estimated melt pool is more than about 15% wider than the container, the wick is oversized for the jar. That is not a safe “extra full” melt pool. It means a large flame, a hot glass wall, sooting, and in a thin container a real crack risk. The calculator flags this separately from tunneling, because the fix runs the opposite way: size down, or switch to a wax with a lower factor.

Testing Is Essential

This calculator provides a starting point, but every candle must be test-burned. Factors like fragrance oil load (which softens wax), dye concentration, ambient temperature, and container material all affect the actual melt pool. Always perform a minimum 4-hour test burn and measure the actual melt pool diameter.