My Jar Has a Narrow Bottom and Wide Top — Why Does the Candle Burn Differently as It Moves Through the Changing Container Diameter?

Area goes with the square: why a small taper matters

The wick doesn't see diameter; it sees surface. A melt pool is roughly a disc, and a disc's area is π × r². Halve the radius and the area falls to a quarter. So a jar whose inside goes from 7.6 cm across at the top to 5.8 cm near the base, which may look like a gentle curve, gives pools of 45.36 cm² and 26.42 cm²: the base band has 42% less surface. The middle, at 6.8 cm, gives 36.32 cm², 80% of the top.

Two consequences follow for a single wick. At the wide top, the wick has more surface to melt than at any other height, so the first full pool is slowest there; the very rough rule of about an hour per 2.5 cm of width says about 3.0 hours at 7.6 cm against 2.3 hours at 5.8 cm (a commonly cited rule of thumb; your log decides). Near the base, the same melting has less surface to spread across, so the pool tends to run deeper, and each gram burned takes the level down about 1.72 times further than at the top band. The flame is also closer to the glass on every side, so the glass tends to warm sooner.

Even CSI's straight-looking 150 g jar tapers on the outside: its page gives a 7 cm outer rim and a 6.5 cm base, which as circles differ by 13.8% in area (38.48 against 33.18 cm²). That is an illustration of the outside only; the inside is what the pool meets, and no CSI listing states an internal diameter. The container series explains how a wider-at-the-top jar changes burn testing (the wider-at-the-top post) and why the internal, not external, diameter is the one that matters (external vs internal diameter). This page gives you the measurement, and the reading of your burn against it.

Taper-related burn patterns, ranked

The order is editorial judgement, most common first; CSI publishes no failure statistics or measured burn data. The point of the table is the last two columns: each pattern either lines up with the profile or it doesn't.

Rows 1 to 4 are the taper doing what tapers do. Row 5 is a different problem that happens to live in the same place, and row 6 is the taper compounding a double wick. The only way to tell rows 1–4 from look-alikes is to have the profile in hand.

Profiling your jar at three heights

Choose three heights, measured up from the inside base: near your fill line (the top band), mid-height, and about 1 cm above the base (where many makers stop a burn, common practice). Mark them on the outside with tape; the Craft Paper Tape is sold for packaging, at ₹4.72 a metre on the 50 m roll, and any masking tape works as well. Then use one of three methods, or two to cross-check.

The water and ruler figures agree to within a millimetre or so in the example, which is as good as home measurement gets; if yours disagree by more, repeat the water step with a larger volume so the rise is easier to read. All numbers here are illustrative.

Setting the profile against the burn

Burn two candles poured from one batch in the profiled jar, on one wick, with the same session length, trim and room, to the stop line. The worked example uses the Shot Glass Jar, CSI 464, Jasmine at 8% of total weight (10.4 g of oil and 119.6 g of wax in a 130 g candle) and Eco C1. The glass page states no hot-pour figure, so follow CSI 464's stated "Pour Temperature 80°C – 90°C" and check the glass with a single test pour before the log candles, since no heat figure is stated; the oil page says to add fragrance to wax "cooled to the recommended pour temperature for your wax type".

Read across the rows. The ring appears in the widest band and closes as the area shrinks; the depth and flame climb as the area falls from 80% to 58%. That is the shape at work. The numbers are illustrative, and the depth and flame are compared with the same candle's middle band, not with a CSI figure. Pool depth rules of thumb (about 0.5–1 cm) are commonly cited, not CSI data. The full depth-by-height chart for any jar is the deep-pool post; burn rate in grams per hour, if the lower burns also seem to go faster, is the weigh-per-burn log.

What the match tells you, and what it costs

Costs are worked examples and exclude labour, freight, packaging and GST. From nothing, the cash outlay is ₹837.00, or ₹1,191.00 with the scale. The profile itself costs nothing but water and time, and in the jar you already use it costs nothing at all. A shot glass at the pack-of-6 unit price is ₹46.40 cheaper per jar than the 150 g jar, but a cheaper glass with an unmeasured taper is not a saving if it needs a wick you can't find.

What not to buy for a tapered jar

A candle that behaves differently at every height invites a new wick at every height. We would rather you measured first, even though the wicks and jars are ours.

What each outcome needs: a taper that explains the burn needs the retest in 3256, usually with wicks you already own. A large area ratio needs a decision about fill height or jar shape. A profile that is nearly straight needs you to look at the wick and the burn habit instead.

Jars, scale, wicks and oil for the profile

Five items: the illustration jar, the worked-example tapered glass, the scale for water steps, the log candles' wick and the worked-example oil. Chosen on page statements, per-unit price and stock on 26 September 2026; CSI has no measured internal profiles or burn data, so nothing is ranked on performance. The oil table shows every size, with 150 g candles at 12 g and 130 g candles at 10.4 g.

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