My Candle Jar Holds 200 ml but Has a 7 cm Internal Diameter — Which Measurement Should I Use When Choosing the Wick?

The wick melts a circle, not a volume

Think about what a wick does in one burn. The flame melts the wax around it, the liquid pool widens, and within a few hours it should reach the wall all the way round. The flame never has to "reach" the bottom of the jar in one sitting; it works down session by session, a few millimetres of pool at a time. So the size of the job, per burn, is the area of the circle the pool must cover. That area is set by the inside diameter at the level where the pool is: π × r².

Capacity in ml is that area multiplied by the height of wax. Double the height and you double the ml without changing the circle at all. That is why ml is the wrong input for a wick. It describes how much candle there is to burn, and says nothing about how wide each burn must melt.

If your jar really holds 200 ml to the brim and really measures 7 cm inside, it is about 5.20 cm deep inside, a fairly short, wide jar. Fill it to 1 cm below the rim and it takes about 161.6 g of water, which by the 0.86 to 0.9 rule of thumb is a candle of roughly 139 to 145 g. That fill weight matters for your wax order and label. It does not move the wick decision by a millimetre. Why two jars of equal capacity diverge is worked through in the same-capacity, different-diameter post; why equal wax in a tall and a short jar needs different wicks is the tall-versus-wide explainer.

What height does change

Height is not irrelevant; it just answers different questions. A taller column of wax burns for more sessions. The flame also sits deeper inside the glass as the candle burns down, where there is less air movement and the glass has been warming for hours, so the last third can burn hotter and with a different flame than the first. That is a reason to run the full burn-down on your chosen wick, not a reason to choose the wick by height. It is also why a thick glass base, which makes the jar look taller than its wax column, deserves its own check in the thick-base post.

Which diameter: the one at pool height

For a perfectly straight-sided jar, the inside diameter is the same from the fill line to the floor, and any measurement below the rim will do. Many jars are not like that. Lug-cap and salsa-style jars commonly have a narrowed neck and a shoulder; apothecary shapes curve; some tumblers taper; heavy jars have a thick base that lifts the floor. In each case, the diameter that matters is the inside diameter at the level of the wax surface, because that is where the pool forms.

For the first burns, that is the fill line, or 0.5 to 1 cm below it (where the pool sits once it has settled). If the jar keeps the same diameter all the way down, you are done. If it narrows, widens or curves, you need the diameter at two or three heights and a decision about which one governs. That decision, and the checkpoints to watch as the pool descends, has its own guides: the jar that narrows toward the bottom for the choice, and the jar that is wider at the top for how the pool behaves as it burns down.

Four ways to measure the inside diameter

You do not need a lab. You need one of three measuring methods and a water check to confirm it. Measure three jars from the same batch, because mass-produced glass varies, and write down the smallest and largest readings as well as the average.

The rise differences are small (a few millimetres between rows), so measure the rise with a ruler held against the outside of a clear jar, or with a marked skewer inside an opaque one. If the water check and the ruler disagree by more than a couple of millimetres of diameter, the jar is probably not straight in that band. Go back to step 1 and measure at two more heights. For opaque or coloured glass, the water-rise check is often the more reliable of the two, because you cannot see the inside wall to line up a ruler.

What CSI jar listings state, and what they don't

Of CSI's 72 container listings, 21 state some diameter and 20 give only a "width". None states an internal diameter. Here are the ones you are most likely to wick, quoted as written, verified 26 September 2026.

Look at the last row. The Matte family and the Green Iridescent jar both carry "7 cm" and hold 200 ml and 300 g respectively. If both really are about the same width, they are candidates for the same wick bracket despite the capacity difference, because height, not width, makes the second jar bigger. That is only a hypothesis until you measure both insides; if it holds, it is the logic behind standardising wicks through diameter.

Now the arithmetic that should make you measure. Suppose the Matte jar's 7 cm is the outside and its walls are about 3.5 mm (our assumption; CSI publishes no wall thickness). The inside is then about 6.3 cm and the pool 31.17 cm², 19% less than a true 7 cm-inside jar at 38.48 cm². A wick bracketed for "7 cm" from the listing is bracketed for a pool nearly a quarter larger than the one you poured. Outside versus inside is taken apart properly in the external-diameter post; how much a few millimetres can move a pool is in the 5 mm post.

From diameter to a bracket, not a wick size

Wick makers commonly publish sizing guides by diameter because diameter is a strong single predictor. It still is not enough to pick one wick, because the same diameter behaves differently with different waxes (soy blends melt differently from paraffin), different oils and loads (heavier or higher loads can make the same wick behave smaller or larger; see the fragrance-load post), different fill depths and even different jar colours. Even CSI's own oil pages say so: the Verbena page tells you to "test wick size based on container diameter". The honest method is to use the diameter to place a bracket, then let the burn choose.

The rungs CSI actually sells

For a 7 cm-inside jar in a container soy such as Luxury Soy Wax CSI 464, a sensible first bracket is C1 / C2 / Cotton Braided: the thin rung that will probably under-melt, the middle that might be right, and the heavy rung that will probably over-melt. That spacing is the point. If the thin rung wins, you have learned your oil and load burn hot; if the heavy one wins, they burn cool; if the middle wins, you have evidence on both sides. How to choose three rungs for a straight 3-inch (about 7.6 cm) jar in more depth is the first-three-wicks post; when a wide jar should jump to two wicks is the 4-inch luxury jar post.

How to read the first burn

Light all rungs at once, side by side, in still air, after the cure your oil page states (the Sandalwood Fragrance Oil page, for example, says "Up to 10% for soy wax, with a cure time of 48-72 hours"). Log the pool every hour. The rules of thumb below are commonly used by candle makers; they are starting points, and yours will shift with wax and oil.

A very rough rule some makers use is about one hour of burn per 2.5 cm of jar width for a full pool; for 7 cm that is about 2.8 hours, which sits inside the common 3-to-4-hour window. Do not stop at the first burn. The shortlisted wick must then burn down the whole jar, in sessions of 3 to 4 hours, with the glass checked in the final third and the burn stopped with roughly 1 cm of wax left (common practice). A wick that is perfect at the top can run hot at the bottom, which is where the thick-base post and the glass-safety cluster take over.

What to buy for a 7 cm bracket

Five items, chosen on what their pages state, price and stock on 26 September 2026. We have no burn data for any of them in your jar, which is the whole reason for the bracket.

A costed bracket, and what skipping it risks

Worked example: three rungs × three jars = nine candles, 150 g each at 8% (12 g oil + 138 g wax; 150 g is the series planning figure for the 200 ml Matte family, so weigh your own jar's fill). Prices are CSI live pricing on 26 September 2026; costs exclude labour, freight, packaging and GST.

With your own jars the kit is ₹1,754.70; with your own jars, oil and centering sticks it is ₹1,040.80. Sandalwood is only a costing example: its page states "Recommended load up to 10% for soy, up to 6% for paraffin", every size in stock on 26 September 2026. CSI 464's page states up to 10%, so 8% sits inside both ceilings; test at your own production load, not ours. Seven Sandalwood grams spare is not enough for a retest, so buy a second 15 g (₹93.22) if a rung needs re-pouring.

What the wrong wick costs at 100 candles

One finished candle in this worked example is a Matte jar ₹70.80 + 138 g of CSI 464 at the 10 kg price ₹70.02 + 12 g of Sandalwood at the 1 kg price ₹60.32 + a C2 wick ₹9.44 = ₹210.58 in materials. A hundred of them is ₹21,058.28, 8.6 times the bracket kit. If they tunnel because the wick was picked for "200 ml", you cannot re-wick a poured candle; you melt out, clean the jars and start again, or sell a candle that leaves a wall of unburnt wax.

Now the other direction. Suppose the bracket says Cotton Braided rather than C1. That wick costs ₹6.10 more per candle, ₹610.00 over 100 candles. A C2 instead of a C1 is ₹3.54 more per candle. The wick is the cheapest line on the bill; buying the right one is never the expensive part. Choosing by the wrong measurement is.

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