How to find the right wick size for your jar

Measure the inside diameter of your jar, find that diameter and your wax on the wick maker's or supplier's chart, and treat the size it gives as one of three candidates: that size, one smaller and one larger. Pour a test candle with each, burn them side by side, and keep the one that gives a full, even melt pool with a steady flame and no soot. A chart is a starting point because it cannot know your fragrance load, dye, jar shape or wax lot. This page shows how to read a chart, what it assumes, the test that settles the size, and a worked example from a named supplier's chart.

What a wick chart is

A wick chart is a supplier's summary of its own tests: for each wax it sells and each container diameter, the wick sizes that burned well in its lab. Northwood, a candle supplier, describes its chart this way: waxes are "listed across the top," and the numbers down the left side "refer to the interior diameter of the container in inches" [1]. Supplies for Candles in the UK organizes its chart by internal diameter in millimeters and inches, with a column for each of its waxes (CocoPro, KeraSoy, Nature C3, ProSoy, ParaSoy and paraffin) and a recommended wick series and sizes in each cell [2].

Every chart is tied to the supplier's own wax and wick lines. A chart for one supplier's soy wax tells you little about another supplier's soy wax, and sizes are specific to a series (a CD 12 and an ECO 12 are different wicks). Use a chart from the company whose wicks you are buying, and the column for your wax or the closest one it lists.

What every chart assumes

Suppliers are candid that their charts are not answers. In their own words:

• CandleScience's recommendations assume a 7.5 percent fragrance load and no dye, and "Dyed or heavily fragranced candles may require a larger wick size than the guide recommends" [3].
• Northwood says the type of fragrance and the fragrance load "can also play a role," names container material, thickness and color as factors, and says its chart "is not intended to be used in lieu of testing your candles" [1].
• Supplies for Candles names fragrance load, fragrance composition, dye, pour temperature, room conditions and container thickness, and says "No wick chart can guarantee performance" [2].
• NI Candle Supplies says fragranced container wax typically burns about 10 to 12 mm wider than its chart states, and tells readers to add 10 to 12 mm to the chart diameter when the melt diameter is not specified [4]. That is NI's note about its own chart, and it shows how much the conditions behind a chart matter.

Wax viscosity matters too. CandleScience found its coconut apricot blend less viscous than pure soy, so it "will generally need a smaller wick than soy wax" in the same jar [5]. That is why the wax column on the chart counts as much as the diameter row.

Measuring the jar

Measure the inside diameter, at the widest point the melt pool will reach. For a straight-sided jar that is any point; for a jar that bulges, narrows at the neck or tapers toward the base, the melt pool's widest point is usually partway down, and you may need different wick behavior near the top and the bottom. Use calipers or a ruler across the opening, and subtract the wall thickness if you measured the outside. Write the figure in both inches and millimeters, since charts use either. How diameter relates to jar sizes is covered on choosing a candle jar size.

If your jar is wider than the largest single-wick row on the chart, you may need two or three wicks, covered on when a candle needs two or three wicks.

The test that decides the size

The method is the same whatever the chart: test the chart's suggestion and one size either side, all at once, under the same conditions. Supplies for Candles advises testing the recommended wick "along with one size up and one size down" [6], and Northwood says to try several wicks from the recommended column "until you find one that works" [1].

1. Fix everything except the wick. Same wax lot, fragrance oil and load, dye, jar and fill height, as your finished candle will have. Record each.
2. Pour at least one candle per size (more if you can, so one bad pour does not mislead you), label each with its wick, and cure them as your wax's data sheet says. GW 464's instructions, for example, ask for 48 hours before test burning [7].
3. Trim each wick the same way before lighting. CandleScience trims to 1/4 inch (6 mm) in its soy tutorial [8].
4. Burn them side by side in a draft-free room, away from each other and from anything flammable. Kohl's protocol 100-Z (February 2025), one published retailer test built on ASTM F2417-17, burns most candles in 4-hour sessions with hourly readings [9]; that is a practical session length for your tests too.
5. Record every hour: melt pool diameter and depth, flame height, flicker or smoke, carbon on the wick, and how hot the jar feels (measure it if you can). Kohl's sets a flame height maximum of 3 inches for most candles [9], a retailer's requirement rather than law, explained on measuring flame height.
6. Let them cool fully, then repeat for several sessions and, for a candle you will sell, burn to the end. Some problems show up only in the lower half of a jar, as the flame gets closer to the glass.
7. Choose the size that passes throughout. Generally, an undersized wick shows a narrow pool and tunneling, and an oversized wick a tall or flickering flame, smoke, heavy carbon and a hot jar. How to read a failed result and move up or down a size is on when to change the wick size.

The full protocol, with pass and fail figures from a published retailer test, is on how to burn test a candle, and what a good melt pool looks like hour by hour is on reading the melt pool.

A worked example from a named chart

Supplies for Candles gives one row of its chart as an example: for a vessel of 50 to 57 mm internal diameter in its CocoPro wax, it lists TCR 21/12, TCR 24/12 or TCR 24/14 as "a starting testing range" [2]. Here is how that becomes a test.

The candle. A straight-sided jar measured at 54 mm inside diameter, filled with CocoPro, fragrance at the load you plan to sell, no dye.

The candidates. The chart has already done the bracketing for you: TCR 21/12 (smallest), TCR 24/12 (middle) and TCR 24/14 (largest). Pour at least one candle with each.

The test. Cure as the wax's sheet says, trim all three the same, and burn side by side in 4-hour sessions, recording hourly.

Reading the results. Suppose that after the first session:

These results are illustrative, to show how to read a test; your own figures decide. In this case, carry TCR 24/12 and TCR 24/14 into further sessions and to the end of the jar. If 24/12 holds a full pool to the bottom without smoke or excess heat, it is your wick for that candle. If it starts to tunnel in the lower half, the larger size may be the right one. If both fail in opposite directions, check your fragrance load and wax before trying a different series.

Your own chart example. CandleScience's beginner tutorial pairs a CD 18 with SimplySoy in a straight-sided tumbler [8], but the tutorial does not give the jar's diameter, so it cannot serve as a sizing example. When you follow a tutorial, measure its jar, and test that wick with one size either side in your own setup.

What changes the size later

Any of these means the size you found needs testing again: a different fragrance oil or load, adding or changing dye, a new jar (even one of the same nominal size from a different maker), a different wax, an additive, or a new wax lot that behaves differently. CandleScience's assumption of 7.5 percent fragrance and no dye [3] is the clearest reminder that a load or color change can move you up a size. The full list is on what has to be retested when you change something.

Keep the results

Write down every test: wax and lot, fragrance and load, dye, jar and diameter, each wick, and the hourly readings. A record that says "24/12 passed in a 54 mm jar at 8 percent of the wax" is what lets you reorder with confidence a year later. Fields and a template are on keeping burn test records. If your jar is wide enough that no single wick fills it, go to when a candle needs two or three wicks; otherwise, go on to how to burn test a candle.

References

1. Northwood, How to Use This Wick Chart (help center article; chart updated November 2023), read October 22, 2026. https://northwood-knowledge.groovehq.com/help/how-to-choose-the-best-wicks
2. Supplies for Candles, Wick Size Chart, published September 14, 2020, modified September 2, 2026. https://www.suppliesforcandles.co.uk/wick-size-chart/
3. CandleScience, Candle Wick (wick category page with series descriptions), read October 22, 2026. https://www.candlescience.com/candle-wick
4. NI Candle Supplies, The Only Candle Wick Guide You'll Ever Need, June 24, 2025, updated September 17, 2026. https://www.nicandlesupplies.com/blogs/how-to-guides/the-only-candle-wick-guide-youll-ever-need
5. CandleScience, Lab Notes: CandleScience Coconut Apricot Wax, undated (images dated April 2024), read October 22, 2026. https://candlescience.com/lab-notes-candlescience-coconut-apricot-wax
6. Supplies for Candles, Candle Wicks (category page with wick finder notes and FAQ), read October 22, 2026. https://suppliesforcandles.co.uk/product-category/candle-wicks
7. Voyageur Soap & Candle, Golden Brands GW 464 Soy Container Candle Wax (product page with manufacturer's instructions), undated, read October 22, 2026. https://www.voyageursoapandcandle.com/Golden_Brands_464_Soy_Wax_p/20264.htm
8. CandleScience, How to Make a Soy Candle, updated October 27, 2025. https://www.candlescience.com/learning/how-to-make-a-soy-candle
9. Kohl's, Test Protocol 100-Z: Candle (including freestanding, taper, tealight, votive, filled and novelty candles), revised February 2025, read October 22, 2026. https://link.kohls.com/content/dam/klink/100-Z-CANDLE.pdf