Which candle wick should you use? A size-by-container guide

The 30-second version: Match wick thickness to container diameter, not to the wax or the fragrance. Too thin tunnels, too thick smokes — and a 100 g spool of thread makes 650–900 candles, which is why serious makers buy spools, not pre-cut wicks.

Every candle maker has lived this one: the first test candle burns a neat hole straight down the middle, leaving a thick wall of untouched wax. The wax gets blamed. The fragrance gets blamed. But nine times out of ten, the culprit is the few centimetres of cotton in the middle.

The one job a wick has

The wick must generate a melt pool (the liquid wax circle around the flame) that reaches the container wall within 2–3 hours of burning. Everything below follows from that. As a working rule for soy wax:

Container diameter	Typical size	Wick guidance
Up to 50 mm	Shot glasses, 100 ml tins	Thin single wick
50–70 mm	200–300 ml jars	Medium wick — the most common size
70–90 mm	300–500 ml jars	Thick single wick, or twin medium wicks
Above 90 mm	Bowls, 3-wick vessels	Multiple wicks, evenly spaced

"Why does my candle tunnel?"

Tunnelling — wax burning straight down the middle — almost always means the wick is too thin for the vessel. Go up one thickness, or split wide vessels into two wicks. And the first burn matters more than people think: let the melt pool reach the wall before you blow it out, or the candle "remembers" the narrow pool and follows it forever after.

"Why does the flame smoke and mushroom?"

The opposite problem — too much wick for the vessel. A flame taller than about 3 cm, black smoke, or a carbon ball on the tip all say the same thing: go one size down, or trim the wick to 5 mm before every burn.

Here's the part that changes your costing

A 100 g spool of cotton wick thread runs roughly 80–100 metres depending on thickness. At 10–12 cm per candle (wick height plus tab allowance), that's 650–900 candles from one spool. Do that maths against pre-cut wicks and you'll see why makers switch to spools the moment production scales.

One catch: raw thread must be primed (dipped in molten wax) before use, or it burns too fast and pulls loose from its base. Making more than a few dozen candles a week? Prime your own from a spool. Testing small batches? Pre-waxed wicks save the step.

So what should you do?

Size off the table above, fix tunnelling by going up and smoking by going down, and buy thread on spools once volume justifies priming. A few quick answers on the way out: cotton wicks work in both soy and paraffin, but soy is denser — moving a paraffin recipe to soy means one wick size up. Wicks don't expire; just store spools dry and away from fragrance oils, which can soak into the cotton and change how it burns. And the wick sustainer? That's the small metal tab holding the wick upright — crimp it onto primed thread and fix it with a glue dot or a drop of molten wax.