A candle that tunnels, smokes or puts itself out is rarely a wax problem. Most of the time, the wick is wrong. Wick sizing is the least glamorous part of candle making, and it is the one that decides whether your chosen jar, wax and fragrance actually work together.

The useful part is that wick size is not a mystery. It comes down to three things you can measure, and once you know them, picking a starting point takes a couple of minutes. After that, it is just testing.

What Actually Determines Wick Size

Every wick decision comes back to the same three variables:

• Wax type and melt point. Thicker, more viscous wax is harder for the wick to draw up, so it needs a bigger wick.
• Jar diameter. The wider the melt pool has to spread, the more heat the wick must produce.
• Fragrance load and additives. Oils, dyes and hardeners all change how the wax behaves as fuel.

Change any one of them and your wick size may need to change too. A wick that performs perfectly in a 70mm soy jar at 6% fragrance can be too small for the same jar in paraffin at 10%.

Wax Type Comes First

Soy and soy blends

Soy wax is more viscous at melt and has a lower melt point than paraffin, so it generally needs a larger wick for the same jar diameter. Container soy blends usually work well with CD, ECO, LX or similar cotton and paper-cored series. If your wax is a soy-coconut blend, expect the behaviour to sit somewhere between the two, and check the supplier's own chart before you buy a whole bag of wicks.

Paraffin

Paraffin burns more readily, so it typically takes a wick one or two sizes smaller than soy in the same jar. It is also more forgiving of a slightly oversized wick, which is one reason it has a reputation for being easy to work with.

Beeswax and hard blends

Beeswax has a higher melt point and needs a noticeably larger wick. Most makers blend it with soy or coconut rather than using it alone in a container, which means your wick size depends on the ratio. Test each blend rather than assuming.

Jar Diameter: Measure It Properly

Measure the inside diameter of the jar at its widest point, in millimetres, at the level where the wax sits. Not the outside, not the neck, and not the base if the jar tapers outwards. A flame radiates out from the wick, so the widest point governs how far that heat has to travel.

As a rough guide, a single wick comfortably handles a jar up to around 75–80mm across. Beyond that, you are usually better off with two or three wicks, or a wooden wick, rather than trying to force one oversized wick to do the work. Two smaller wicks also give a more even pool in wide or square vessels.

Fragrance Load and Additives

Fragrance oil is heavier than wax. The more you add, the harder the wick has to work to pull wax up through the fibres, so a higher load often means going up a size. Moving from 6% to 10% is enough to change things noticeably.

Dyes matter too. Liquid dyes and solid colour blocks can clog a wick, and too much dye is a common cause of soot and a struggling flame. Additives such as stearic acid raise the melt point and usually call for a larger wick, while UV inhibitor has a smaller effect. If you use several additives at once, expect to test again.

A Simple Starting Chart

These are starting points, not answers. They assume a soy or soy-blend container wax with 6–8% fragrance, a room at normal temperature, and a wick trimmed to about 5mm.

• 50–60mm jar: CD 4–6, ECO 2–4, LX 12–14
• 60–70mm jar: CD 6–8, ECO 4–6, LX 14–16
• 70–80mm jar: CD 10–12, ECO 6–8, LX 18–20
• 80–90mm jar: CD 14–16, ECO 8–10, LX 22–24
• Over 90mm: move to two or more wicks

For paraffin, start one or two sizes smaller. For beeswax blends or a heavy fragrance load, start one size larger. Wick numbers are not standardised between manufacturers, so always cross-check with the chart that comes with your wax.

Test Every Wick You Are Considering

1. Pour at least three candles: your calculated size, one size up and one size down. Keep wax, jar, fragrance load and cure time identical.
2. Let them cure properly — for soy blends, that usually means several days.
3. Trim each wick to about 5mm before every single burn.
4. Burn in sessions of no more than four hours. Note the melt pool at one, two, three and four hours.
5. Record the pool width, flame height, any soot, and whether the flame flickers, dances or mushrooms.
6. Burn one test candle all the way to the end. The last third is where weak wicks give themselves away.

Reading the Signs

After two or three burns, the candle tells you what it needs.

• Wick too small: tunnelling, wax clinging to the glass, a small flame that drowns in the melt pool, or the flame going out on its own.
• Wick too large: soot on the glass or rim, a tall flickering flame, a jar that gets uncomfortably hot, heavy mushrooming, and a fast, hot burn.

One exception: a thin ring of unmelted wax on the very first burn is normal. If it has not caught up by the third burn, go up a size.

Start Narrow, Then Trust Your Testing

Buy a small selection of wick sizes in one series rather than a mixed bag, and keep a notebook or spreadsheet with the jar, wax, fragrance load, wick size and result. Once a combination performs, write it down and treat it as fixed. If you later change wax, jar supplier or fragrance load, retest — and if you sell your candles, keep those records alongside your safety documentation.

Photo: 51581 / Pixabay