You’ve poured a candle that smells unreal in the jug, looks glossy in the jar, then it lights… and either tunnels like it’s trying to escape or mushrooms into a smoky mess. That’s not your fragrance oil “not being strong” or your wax being “bad”. Nine times out of ten, it’s simply the wick.
Wick size is the engine of a candle. Too small and you’ll never get a full melt pool, so hot throw is muted and customers complain it “doesn’t smell”. Too large and the flame runs hot, fragrance burns off faster, soot appears on the jar, and your candle can fail basic safety expectations. If you’re selling, this is one of the quickest ways to protect your reviews.
Which wick size do I need? Start with the container, not the wax
The most reliable starting point is the internal diameter of your container at the fill line. Wick charts are built around vessel width because that’s what the flame needs to heat - the surface area of wax.
Measure across the inside of the jar (in mm) where the wax will sit. If it’s a tapered jar, measure at the top of the wax, not the very top of the glass. If it’s a wide, shallow vessel, treat it as “wide” even if the total wax weight is low.
From there you choose a wick series and a rough size. That’s the beginning, not the finish. Two jars can have the same diameter but behave differently because of glass thickness, headspace, and whether they hold heat or shed it.
Why wax weight can mislead you
Makers often ask for a wick based on “200g candles” or “30cl jars”. But a tall, narrow 200g jar may wick smaller than a short, wide 160g tumbler. Weight is about volume. Wicking is about surface area and heat management.
The four factors that change wick size (fast)
If you’ve ever followed a chart and still got tunnelling or sooting, it’s because the chart didn’t know your full recipe and environment. These are the levers that push you up or down a size.
1) Fragrance load and fragrance type
More fragrance oil usually needs more heat to maintain a stable melt pool, so it can push you towards a slightly larger wick. But it’s not a simple “more oil = bigger wick” rule.
Some fragrances are naturally heavier (think bakery, resins, musks) and can thicken the melt or affect capillary action in the wick. Others are bright and volatile (laundry/fresh styles) and can throw well without forcing you to over-wick. If your candle smells strong cold but weak hot, don’t automatically jump two sizes - check your melt pool and burn temperature first.
2) Wax type and additives
Different waxes melt and transport heat differently.
Soy tends to like a steady, slightly larger wick than you’d expect for a clean full melt pool, especially in wider jars, but it also punishes over-wicking with frosting and soot if you push it too far.
Paraffin generally throws strongly and can achieve a full melt pool with less wick, but can also run hotter. Many blends (soy-paraffin, rapeseed-coconut, etc.) sit in the middle.
Additives like stearic, vybar, or even heavy dye loads can change viscosity and burn characteristics. If you’re heavily colouring for brand identity, accept that you may need to re-test wicks when the shade changes.
3) The container and lid behaviour
Thick glass and heavy bases hold heat and can make a wick behave “bigger” after a few burns. Thin glass sheds heat and can make a wick behave “smaller”. Airtight lids can also trap fragrance in the headspace between burns, which affects customer perception of strength, but not the actual melt pool.
If you sell in tins, remember tins reflect heat back into the wax. That often reduces the wick size needed compared with an equivalent glass diameter.
4) Real-world airflow (aka your customer’s living room)
A candle that behaves perfectly on your test bench can soot on a windowsill, in a draughty hallway, or under an extractor fan. If your target customer is likely to burn candles in busy spaces (kitchens, open-plan rooms), build a little tolerance into your testing and avoid wicks that are “right on the edge”.
Reading the candle: what “correct wick” actually looks like
Wick charts can only get you close. The candle tells you the truth.
A well-wicked container candle typically has a flame that’s steady, not wildly dancing. The melt pool should reach close to the container wall in a reasonable time without becoming excessively deep.
Depth matters because it reflects heat. A very deep melt pool means the system is running hot, which can increase soot and speed up consumption. Too shallow means the flame can’t feed properly and tunnelling sets in.
Signs your wick is too small
You’ll see a melt pool that stays narrow, leaving a thick wax wall around the edge after 2-3 hours. Hot throw will be disappointing because not enough fragranced wax is being warmed and evaporated. The flame may look weak, and you might see the wick drowning near the end of a burn cycle.
Signs your wick is too large
Look for a very tall flame, smoking, mushrooming (carbon ball on the tip), excessive flicker, or soot marks on the jar. The melt pool may reach the sides quickly but become too deep. Customers might say the candle “burns too fast” or smells strong at first then fades - overheating can drive off fragrance and change the scent profile.
A practical wick testing routine that saves you money
If you’re asking “which wick size do I need”, the most honest answer is: pick a sensible starting point, then test two sizes either side. That’s how you get repeatable results you can scale.
Test at least three wicks in the same jar and recipe. Keep everything else identical: wax, fragrance %, dye, cure time, and pour temperature. Trim wicks to the same length before every burn.
A realistic burn schedule is 3-4 hours per session, with full cooling between sessions. That mimics how customers actually burn candles and stops you making decisions based on a one-hour “first light”.
During testing, note:
- Time to reach a near-full melt pool
- Melt pool depth at 3-4 hours
- Flame height and stability
- Sooting or smoke on extinguish
- How the candle behaves mid-way and near the bottom (many issues show late)
Common “it depends” scenarios (and what to do)
Wide jars that refuse to pool
For very wide containers, a single wick can struggle without over-wicking. The answer isn’t always “bigger wick”. Sometimes it’s a different wick series designed for wider diameters, or moving to double wicking with smaller wicks spaced correctly. Double wicking is a separate test programme, but if your brand uses wide statement jars, it can be the cleanest route to strong throw without soot.
Natural wax candles with ‘weak’ hot throw
If your melt pool looks good but hot throw is still light, don’t blame the wick first. Check cure time, fragrance compatibility, and whether you’re pushing fragrance load beyond what the wax can hold cleanly. Overloading can reduce performance and cause sweating, even if the scent is “strong” in the bottle.
Black soot only happens on certain scents
That’s real. Some fragrance profiles and certain components are more prone to sooting when the system runs hot. If one scent is sooting and your others are clean in the same jar, test one wick size down for that fragrance only. It’s normal for a range to need more than one wick size even in identical packaging.
Choosing wick types: cotton, stabilised, wooden
Cotton and stabilised core wicks are popular because they’re consistent and easier to dial in across a product line. Wooden wicks can give a premium look and a distinctive crackle, but they’re less forgiving: they can struggle with heavier fragrances, need very specific trimming, and can fail if the melt pool doesn’t support them.
If your priority is reliable performance and fast replenishment for customer favourites, start with a proven cotton-style series and build your testing library. Once your bestsellers are locked, then experiment with wooden wicks as a design choice, not a rescue plan.
If you’re selling: wick size affects compliance and customer trust
In the UK market, customers expect candles to burn cleanly and safely. A candle that soots heavily, produces excessive smoke, or overheats the container isn’t just a returns headache - it can put your whole brand under a spotlight.
That’s why makers who treat wicking as part of their product development (not an afterthought) scale faster. Strong scent throw is great. Strong, consistent burn behaviour is what earns repeat orders.
If you want a supplier that’s set up for makers who move quickly - fragrance oils, consumables, and practical support like free CLP labels - Craftiful is built for that, with same working day dispatch before 11am and next day UK delivery on eligible orders via https://www.craftiful.co.uk.
The fastest way to get to “correct wick”
Pick your jar, measure the internal diameter, choose a sensible starting wick, then test up and down one size with your exact recipe. Aim for a stable flame, a near-full melt pool without excessive depth, and a clean jar after multiple burns.
The best part is this: once you’ve done it properly for one container and wax system, you’ve created a repeatable foundation. Every new fragrance becomes a quick confirmation test, not a full reinvention. And that’s how you spend less time babysitting test burns, and more time building a range customers come back for.
