I'm Switching Candle Jar Suppliers but the New Jar Looks Almost Identical — What Measurements Must Match Before I Keep the Same Wick?

Why "almost identical" is the risky case

When a new jar is clearly wider or taller, nobody keeps the old wick without a test. The trouble comes when the new supplier's jar has the same silhouette, the same listed dimensions and the same capacity. The listing matches, so the maker changes the jar and nothing else, and the first sign of a problem is a customer's candle tunnelling, or a jar that runs hotter in the last third than anything you tested.

Outside dimensions hide the three things that change a burn. Wall thickness decides how much of the outside width is glass and how much is wax: 1.5 mm more glass on each side takes 3 mm off the inside diameter. Base thickness decides where the floor is, so it changes the depth of wax and how close the flame gets to glass at the end. Taper decides whether the pool your wick must melt stays the same size as the candle burns down. None of these is printed on a typical listing, and a mould can differ in all three while the outside matches to the millimetre.

Even one supplier's near-identical listings disagree

We checked our own. CSI's Clear Glass Jar with Golden Lid (150 gram) states "Height 8cm, outer diameter 7cm" and a base diameter of about 6.5 cm; elsewhere on the same page the 8 cm becomes "height with lid". Its coloured sisters, such as the Black Glass Jar with Black Lid (150 gram) (its title still carries a stale "Deliveries Starting 5th Dec" and its text mentions a golden lid, so confirm details on WhatsApp), state the same diameters but only a with-lid height, so the glass body is shorter than 8 cm by however tall the lid is. And our White Matte Glass Jar is listed "Height 8 cm width 7 cm" with "a fill weight of 200 ml", the same headline numbers as the 150 g jar with a different capacity wording. Three listings that look interchangeable on paper; you would not know from any of them what the inside measures. If our own catalogue needs measuring, so does any supplier's.

This guide is about the moment of switching: one old jar you have proven, one new jar you have not. The questions to ask a supplier so the jar stays the same for years are in the long-term supplier questions; keeping a range safe if a jar is discontinued is the continuity plan; and batch-to-batch drift from the same supplier is the batch-variation guide.

The eight measurements, and how to take each one

Take every measurement on five jars from each supplier, not one, because mass-produced glass varies between pieces. Write both sets on one sheet. The "match band" column is our working judgement for jars around 6 to 8 cm across; wider jars tolerate a millimetre more for the same change in pool area, narrower jars less (the maths is in the 5 mm guide).

Measuring the inside without special tools

A calliper with inside jaws is the easiest tool; CSI does not sell one, and a basic vernier or digital calliper from a hardware shop is enough. Without one, a steel rule laid across the opening reads a straight jar's inside diameter to about a millimetre. For the base, stand a rule inside, read the internal depth, and subtract it from the outside height. For the wall, measure across the rim with the calliper, or subtract the inside diameter from the outside diameter and halve it. That is only valid if the jar is straight; a jar with a lip or a shoulder needs the calliper. Why the outside figure cannot stand in for the inside one is covered in the external-versus-internal guide.

The water-rise check for the inside at depth

For the lower diameter in a deep jar, water does what a rule cannot reach. Tare the empty jar, pour in water to exactly 2 cm deep (mark it on the outside with tape), and weigh. In a straight section, grams of water divided by 2 gives the inside area in cm², and the diameter follows from it. Worked example: 62.3 g of water in 2 cm means an area of about 31.2 cm², which is a 6.3 cm circle. Do the same in the old jar; if the grams differ by more than a few, so do the insides. Dry both jars fully before they see wax.

Worked example: two "8 × 7 cm, 200 ml" jars from two suppliers

Jar A is the jar your wick was proven in. We use the series' standard worked-example jar: listed 8 cm high and 7 cm wide, treated as straight-sided with 0.35 cm walls and a 1 cm base, so the inside is 6.3 cm across and 7 cm deep. Jar B is from the new supplier and is listed identically. On the bench, its walls average about 0.5 cm (thicker towards the floor), its base 1.4 cm, and it tapers slightly: 6.1 cm across near the top of the pool, 6.0 cm at the middle, 5.9 cm near the floor. Every figure is illustrative, chosen to be the kind of difference a heavier mould produces.

Now the depth. With a 1 cm headspace, jar A has 6 cm of wax above its floor; jar B, with a floor 4 mm higher, has 5.6 cm. Combine a smaller circle with a shallower column and B holds about 15% less candle to the same fill line. If A gives you the series' planning figure of about 150 g, B gives about 127 g. Your label, your wax order and your load in grams all move with it (see the fill-weight hub for weighing it properly).

What the old wick is likely to do in jar B

Your wick was sized to melt a 6.3 cm pool to the glass in a first burn of about 3 to 4 hours (a common rule of thumb). In jar B the pool it must melt is 6.2% to 12.3% smaller, so the same wick is, in effect, a size larger for this jar. Expect the pool to reach the glass sooner, run deeper than the 0.5 to 1 cm many makers aim for, and the flame to stand taller. In the last third, with a narrower bottom and a thicker base holding heat, the glass is likely to run warmer than anything you saw in jar A. Those are tendencies to test, not certainties; a wax, oil or wick with more margin may shrug it off. The thick-base effect is taken apart in the thick-base guide.

Reverse the example and the risk flips. If the new jar is 2 to 4 mm wider inside, the old wick is effectively a size smaller: a pool that reached the glass in jar A may leave a ring of wax in jar B, and a ring on early burns is the start of tunnelling. Either direction is a reason to test; neither is a reason to guess which way to move.

How close is close enough: our working match bands

Pool area grows with the square of the diameter, so small differences compound. On a 6.3 cm inside diameter, 1 mm wider makes the pool 3.2% larger, 2 mm 6.4%, 4 mm 13.1% and 5 mm 16.5%. Those percentages are why we use the bands below. They are our judgement for jars of roughly 6 to 8 cm, not a published tolerance; there is no universal millimetre figure, and the side-by-side burn overrides the table every time. How to set bands across a range of different jars is a different question, answered in the one-wick-across-jars guide.

The confirmation burn: new jar against old, side by side

This is the short test for a jar that has measured within the first band. It is short because it asks one narrow question, "does the new jar burn like the old one with everything else unchanged?", not "which wick is right?". It needs four candles: three in new jars, one in an old jar as the control.

Pass: the new jars reach the glass within about the same time as the old one, pool depth and flame are close, and the burn-down finishes without the final third running hotter than your old jar's. Fail: any clear difference. A failed confirmation burn is not a disaster: it tells you to run the three-wick test in the middle band, and you have already measured everything it needs.

A fragrance change during the switch muddies the test: change one thing at a time. If you are also changing oil, run the jar test first and the oil later; why oils can need different wicks is in the fragrance-and-wick guide.

What to buy for the check

Five items, chosen on what their pages state, price and stock on 26 September 2026. CSI publishes no burn data for any jar, so none of this is a performance ranking; it is what the measuring and confirmation burn need.

What checking costs, and what skipping it risks

Worked example for a maker switching an 8 × 7 cm line to CSI's Matte jar, costed at CSI live pricing on 26 September 2026. Costs exclude labour, freight, packaging and GST.

Switching to the 150 g apothecary jar instead? The same kit with a pack of 10 Clear 150 g jars is ₹1,604.80; the extra jars give you a spare set for a burn-down in each wick you test. Wax is flat per gram on CSI 464 from 1 kg to 10 kg (₹0.51 at 1 kg, ₹0.51 at 10 kg; the 500 g is ₹0.52), so buying more wax for the test saves nothing per gram.

Set against a reorder

Suppose the switch is for a 200-jar reorder. Two hundred Matte jars are ₹14,160.00, and the wax in them at 150 g and 8% is 27.6 kg, ₹14,004.24 at the 10 kg price. The confirmation kit is 7.2% of the jar bill alone. And if the check does move you a rung, from C1 to C2 across 200 candles, the extra wick cost is ₹708.00; the cost of finding out from customers is refunds, reviews and a reorder you cannot sell.

Frequently asked questions