There’s No Way to Know Which Wick Is Right Except to Burn One
Same wax, same vessel, same fragrance — change the wick and you get a completely different candle. Here’s how to test properly, and why you have to do it far more often than anyone wants to.
Everything else about a candle can be right and the candle can still be bad. The wax can be good, the vessel can be beautiful, the fragrance oil can be excellent and correctly dosed — and if the wick is wrong, the result is a candle that tunnels down the middle leaving an inch of wax up the sides, or one that runs a tall flame, sooties the glass and mushrooms at the tip. There is no calculation that settles this, no chart that removes the need for it, and no way to know in advance. Candle wick testing is the one part of the craft that can only be resolved empirically: you burn one, you write down what happened, and then you know.
What “too small” and “too big” actually look like
Two failure modes, and they’re easy to recognize once you know what you’re looking at.
Too small: tunnelling. The melt pool never reaches the edge of the vessel. Wax builds up in a ring around the sides, the flame sits down inside a well, and the candle burns out early with a substantial amount of wax never used. Customers describe this as the candle “not burning properly,” and they’re right.
Too big: too hot. The flame runs tall and restless. The glass darkens with soot. The wick tip mushrooms into a black bulb. The container gets hotter than it should. Beyond the aesthetic problems, an overly hot candle is a genuine safety concern.
In between those two, there’s a wick that produces a full melt pool with a controlled flame. Finding it is the job.
Measure, don’t eyeball
The reason to run a structured test rather than just lighting one and having a look is that “it seems fine” is not a record, and it doesn’t survive a month.
The measurements worth taking, hour by hour:
Melt pool diameter against vessel diameter. This is the key number, and it’s best expressed as a percentage. A common working approach treats a melt pool under about 90% of the vessel as tunnelling, 90–95% as nearly there, and 95% or more as a pass — provided the flame is behaving.
Flame height. A flame that stays modest is doing its job. One that runs long is a sign the wick is oversized for the wax and vessel, regardless of how good the melt pool looks.
Sooting and mushrooming. Both point the same way: too much fuel for the flame.
And the hour. This matters more than people expect. A wick can look like it’s tunnelling at hour one and reach full melt pool by hour three — which is normal, and quite different from one that never gets there at all. Recording hour by hour is what distinguishes “slow” from “wrong.”
Worth saying clearly: figures like 90%, 95% and a flame under 20mm are common working targets, not standards. Different waxes, vessel shapes and makers use slightly different thresholds. What matters is that you apply the same criteria consistently to every test, so your results are comparable to each other.
The rule beginners hate
Here is the part that people resist hardest, and it’s the most important thing in this article.
If you change the wax, the vessel, the fragrance, or the fragrance load — you test again.
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Not “probably fine because it’s a similar vessel.” Not “same wax, so the wick will carry over.” Each of those four variables changes how the wax melts and how much fuel reaches the flame, and a different fragrance oil at a different percentage genuinely can need a different wick in the same jar.
That’s why a proper test log ends up with a hundred rows rather than ten. It feels excessive right up until the first time you sell a batch that tunnels, at which point it feels obvious.
The consolation: once a combination passes, it’s settled permanently. You never have to test that wax-vessel-fragrance-load combination again, as long as nothing about it changes. The work is front-loaded, and the record is what makes it a one-off rather than a recurring guess.
Test the way it’ll actually be used
A few practical points that make results meaningful:
Test the real vessel, not a similar one. Diameter and glass thickness both matter.
Test at the fragrance load you’ll actually sell at, not a plain wax version. Fragrance oil affects burn behaviour, which is the whole reason the load is one of the four variables.
Let it cure first. Testing a candle the day after pouring doesn’t tell you about the candle you’ll sell.
Burn for a realistic session. Multiple hours, the way a customer would, rather than twenty minutes and a verdict.
Never leave a burning test unattended, and follow the safety guidance for every material you’re using.
And write down the failures
The strongest argument for a written test log is that the failures are the useful part.
“CD-10 tunnels in this vessel” is permanently valuable information. It removes an option, narrows the field, and stops you buying that size again for that jar. Unrecorded, it’s a vague memory that one of the smaller ones didn’t work, which is no use at all.
The same is true of everything else in candle making. A batch that failed tells you where the boundary is. A batch that was merely okay tells you what “not quite” looks like. Only recording the successes throws away half your information — and it’s the half that was expensive to acquire.
An important note
To be clear: this is a general perspective on record-keeping and testing method. It is not safety, chemical, formulation, regulatory, legal, or business advice, it is not training, and it guarantees no outcome. Any wicks, waxes, vessels and figures mentioned are illustrative examples, and wick and cure figures are common working targets rather than standards. Fragrance maximum usage rates are set by the fragrance supplier, differ per fragrance and per application, and must be obtained from them. Follow the safety data sheet for every material you use, and never leave a burning candle unattended. Candles are consumer products subject to safety, labeling, registration and record-keeping requirements that differ substantially by country and change — establish and comply with the ones that apply where you make and sell before selling anything, and consider product liability insurance.
If you want the verdict read back to you
I built a wick burn-test log into my candle and soap making batch log in Google Sheets — melt pool recorded as a percentage of vessel diameter, flame height and sooting hour by hour, and an automatic verdict of TUNNELS, NEARLY, PASS or TOO HOT from your own numbers, with 113 rows because you’ll need them:
👉 Candle & Soap Making Batch Log for Google Sheets & Excel
Whether you use mine or a notebook, test properly and write it down — including the wicks that failed. There’s no shortcut here and there never will be. Burn one, measure it, record it, and the answer is yours permanently. 🕯️
This reflects my own perspective and describes a record-keeping tool — NOT safety, chemical, formulation or regulatory advice, and it is not training; figures shown are common working targets, not standards. Follow the safety data sheet for every material, never leave a burning candle unattended, and establish the rules where you sell before selling anything. Makers: how many wicks did it take to settle your standard jar? Tell me in the comments.
