I Want to Change My Jar from 7.5 cm to 8 cm Internal Diameter — Is a 5 mm Difference Enough to Justify Retesting Every Fragrance?

What 5 mm does to the pool

Your title gives internal diameters, so we use them directly; if your figures came from a listing, measure the inside at the rim, the middle and about 1 cm above the base first. Pool area is π r² on the inside radius; the figures below are geometry, not burn predictions. The general maths of a 5 mm change, across diameters, is the 5 mm post; here we only need this one step.

For scale: a 1 mm difference between two lots of the same 8 cm jar changes the pool by about 2.5%; going from 7 cm to 8 cm, as in the 7 to 8 cm post, changes it by 30.6%. The 7.5 → 8 step sits between those, which is why it gets its own scope rather than either answer. Drift between lots of what is meant to be the same jar is the incoming-lot post.

The pool-area change sets the level of risk

Set your bands in advance and write them down. Ours, labelled as judgement for a soy container range on one wick system:

At 13.8% you are near the top of the middle band. That is a reason to be strict inside the triage, for instance by counting "edge on burn 3" as borderline rather than comfortable, not a reason to jump bands. Anything else that changes with the jar moves you up a band whatever the area says: a thicker base, a strong taper, a different glass, a new fill height or a wick count change. If the new jar is also taller, the final third sits lower and burns longer; treat it as a new system.

Sort the approved list by group and margin

For each approved oil you need two things from the old records: its behaviour group (oils that behaved alike on the house wick) and its margin, how far it was from failing and in which direction. A useful margin note is the burn on which the pool first reached the wall, plus the trimmed flame height. Our worked example is twelve oils, all approved at 7.5 cm on Eco C2 in Luxury Soy Wax CSI 464 at 8% (CSI 464's page: "Fragrance Load Up to 10%").

How the representatives were picked: in each group, the non-borderline oil whose 7.5 cm pool was slowest, with ties broken by base-note weight (our reading of each page's stated notes). So Lavender ("soft musk base") speaks for the light group, Bergamot Amber for the fresh/fruity group and Woody Oud for the heavy group. Borderline oils are not representatives; they are retested in their own right. All loads sit inside both ceilings at 8%; Fresh Strawberries' page states "6-9%", the lowest maximum here, and 8% is inside it.

The triage table: retest, screen or carry

Running the triage

The carry-over check is not a formality. A carried oil goes into production on its group's evidence, and the first batch's full-life candle is the moment that evidence is confirmed for that oil. If it disagrees with its representative, stop pouring that oil and retest it as borderline. The scheduling of a retest like this across a whole range, with more oils than candles, is the same logic as the grouping post.

Three ways to retest, costed

All three plans use 225 g candles at 8% (18 g oil + 207 g wax), oils at their 500 g per-gram prices (the stock you already hold for production), CSI 464 at the 10 kg price and CSI's flat per-wick prices: C1 ₹5.90, C2 ₹9.44, Cotton Braided ₹12.00. Jars are excluded because they are yours; count them as one per candle.

The triage uses 42% fewer test candles than checking every oil and 81% fewer than re-bracketing, and saves ₹1,807.84 in materials against the full check. The bigger saving is burn time: every full-life candle in an 8 cm jar is many sessions of supervised burning, and the triage puts those hours on the six oils where a failure is plausible.

Reading the retest: when a representative fails

The vanilla case has its own deep-dive at 8 cm, a one-rung-up comparison judged in the lower third: the 8 cm vanilla post. The two-burn catch-up logic that makes "edge on burn 3" a borderline note rather than a fail is the 7.5–8 cm hub. If several groups fail together, the problem is the system, not the oils; the diagnostic for a lot that is only a few millimetres wider is the few-millimetres-wider diagnostic.

Buying for the retest

Four items, chosen on page wording, price and stock on 29 September 2026. CSI publishes no wick-performance data, so nothing is ranked on burn results; oil yields are counted at 18 g per 225 g candle.

Frequently asked questions