I’m Double-Wicking a 9 cm Jar — How Far Apart Should the Two Wicks Be Positioned Before I Begin Comparing Wick Sizes?

Start from the inside, not the listing

Every distance on this page is measured to the inside of the glass, because that is where the pool stops. Nothing on the listings will give you that: none of CSI's 72 container listings states an internal diameter, and CSI lists no jar at 9 cm at all, so your jar is your own. Measure the inside across the rim, twice at right angles, and again at mid-height and near the base with a strip of card curled inside the jar (overlap length ÷ 3.14). If the three heights differ, set the wicks for the height where the first burns happen, near the top of the wax, and note the rest. The external-versus-internal argument is made in full in the external diameter post; here is the double-wick version.

A 3.5 mm difference per side sounds trivial. At the wick positions it isn't: if you plan for 9 cm inside and the jar is 8.3 cm inside, a pair set 4.5 cm apart sits 1.90 cm from the glass instead of the 2.25 cm you planned, and every decision you make afterwards about "too close to the glass" is made on the wrong numbers.

Two geometric starting points, and the one to use

With two wicks on a diameter, symmetry does most of the work: each wick serves its own half of the pool, 27.05 cm² here. What's left is how far out along that line to put them. Two pieces of geometry give reasonable first answers. Neither predicts how a candle burns; both give you a defensible number to hold constant.

The halfway rule (s = r) is the working choice on this page. Each wick has the same distance to the centre as to the glass along the line, 2.075 cm here, so neither the middle nor the ends of the line are favoured before you have any burn data. Rounded to a markable 4.2 cm (21 mm either side of the centre), it puts each wick 2.05 cm from the glass along the line. The centroid rule puts each wick at the centre of mass of its half of the pool, 0.424 of the radius out from the centre, which gives 3.52 cm. It is a closer, more "inward" start; use it if your jar tapers inward towards the base, where a pair set wider can end up close to the glass lower down.

Two geometric facts to keep in mind while you set up. Along the wick line the glass is close; at right angles to it, it is not: at 4.2 cm apart each wick is 4.65 cm from the walls at right angles to the line, more than twice its 2.05 cm to the glass along it. That is why pairs so often leave a ring on the short axis, and why the ring shape tells you more than the ring size (the 10 cm ring-shape map reads it). And the wider you set the pair, the closer the flames get to the glass along the line; how far is too close is not a number we can give you, and the wall-gap trade is where that balance is tested.

Putting the tabs where you meant

About the Steel Wick Holder. It is the obvious CSI tool for a pair: its page says "3-hole layout fits single, double, or triple wick setups" and "up to 9 cm wide". But the holes are fixed, in a line, and the page states no pitch. If its outer holes are 42 mm apart, it is exactly what you need. If they are, say, 30 or 50 mm apart, using them sets your pair at the holder's spacing, not the one you planned. Measure it before you use it for this test, or ask us for the figure. A jar measured 9 cm outside is at its stated width limit, so check the fit on your rim too.

Checking the spacing after the pour

Measure every candle before it goes into cure. The flame sits where the wick is at the surface, not where the tab is at the base, so a wick that leaned during the pour burns at a different spacing from the one you stuck down. Two millimetres sounds small; at 42 mm it is 5% of the spacing, and a wick that drifts 2 mm toward the glass has only 90% of its planned wall gap left.

Don't straighten a set candle by pushing the wick through firm wax; it cracks the surface and loosens the tab. Mark it off-spec and pour another. Off-spec candles still teach you something (burn one and watch which side runs hotter), but keep them out of the size comparison. Then cure: many soy makers wait about a week before judging; the British Rose page states no cure time in the text we captured, and the 25 of 102 CSI oil pages that do state one say 48–72 hours for soy.

Only then: comparing sizes at that spacing

With the spacing fixed at about 4.2 cm, the first comparison is the one the question is really about: a C1 pair against a C2 pair, two candles each, everything else held: same jar batch, 300 g fill, British Rose at 8% (24 g of oil + 276 g of wax per candle), CSI 464, cure and room. Burn three sessions of 3–4 hours (about 3.3 hours by the rough one-hour-per-2.5 cm rule), in still air, trimmed alike; log width on both axes, depth at the midpoint, flames, soot and any flame lean toward the glass. Never judge the glass by touch.

The last two rows are where spacing comes back in, and each has its own post: two wicks set too close making one hot centre is the spacing ladder; a strip left between the wicks is the inward repositioning ladder; and a pair that melts the centre but leaves the outside edge, where you can't tell spacing from size, is the spacing × size 2×2. If you haven't yet decided whether this jar needs two wicks at all, start with the both-builds opening round, and for when a pair makes the pool very deep, depth-width decoupling.

Cost of the comparison. Four candles consume 96 g of British Rose (₹328.32), 1,104 g of CSI 464 (₹560.17), four C1 and four C2 (₹61.36) and eight stickers (₹20.00): ₹969.85, jars not included. Per candle that is ₹238.92 on a C1 pair and ₹246.00 on a C2 pair (₹82.08 of oil, ₹140.04 of wax, stickers ₹5.00). From nothing, the cash is ₹1,422.00 (British Rose 100 g, CSI 464 1 kg and 500 g at ₹767.40, C1 20, C2 10, a sheet of stickers), or ₹1,672.00 with a set of five Steel Wick Holders. The 100 g leaves 4 g; the wax leaves 396 g. All figures exclude labour, freight, packaging and GST.

What to buy, and what to skip

Five items, in the order you need them, chosen on page statements, price and stock on 29 September 2026. CSI publishes no wick-performance data, so nothing is ranked on burn results. Oil candles are counted at 24 g (300 g fill) and 12 g (150 g).

Skip: the Wick Centering Device for this job; its page describes one "Hole Dia 0,15" (4mm)", made for a single wick. Skip Cotton Braided; this page is about placing a pair, and a single is a different build. Skip CSI's Apothecary Glass Candle Jar with Dome Lid as a stand-in: it states about 10 cm, not 9, so setting up in it tells you nothing about your jar. And skip bigger wick packs until a pair passes its full life; per-wick prices are the same in every pack.

Frequently asked questions