A percentage is nothing without its denominator
"Eight percent fragrance" is the most commonly repeated instruction in candle making and one of the most commonly misread. Eight percent of what? Almost every wax technical data sheet, and almost every recipe written by a candle maker, means eight percent of the wax weight: 1.28 oz of oil per pound of wax. A minority of suppliers, and most people coming from soap making or cosmetics, mean eight percent of the finished weight, which is a different and smaller quantity of oil.
The gap is not trivial and it grows with the load. At 8%, the wax basis gives 6.40 oz on a 5 lb batch and the total basis gives 6.96 oz — nearly nine percent more oil, and enough to push a wax past its stated ceiling. This calculator asks which basis you mean, computes on it, and then shows you the same batch expressed the other way so you can compare a recipe against a data sheet without doing the conversion in your head.
Everything here is by weight. Fragrance oils differ in density, so measuring by volume introduces an error that varies from one oil to the next. A scale reading to 0.1 g is the single most useful piece of equipment in a candle workshop.
Converting between the two bases, and why the wax ceiling is a wax basis number
On a wax basis the arithmetic is one multiplication: FO = wax × L. Five pounds is 80 oz, and 80 × 0.08 = 6.40 oz. The convenient shortcut every candle maker learns follows immediately — ounces of oil per pound of wax is 16 × L, so 8% is 1.28 oz per pound and 6% is 0.96 oz per pound.
On a total basis you have to solve for the oil, because the oil is part of the total you are taking a percentage of. If FO = L × (wax + FO), then FO(1 − L) = L × wax, so FO = wax × L ÷ (1 − L). At L = 0.08 that factor is 0.08 ÷ 0.92 = 0.08696, so a total-basis 8% is a wax-basis 8.696%.
Going the other way, a wax-basis load L is a total-basis load of L ÷ (1 + L). A wax-basis 8% is 8 ÷ 108 = 7.407% of the total. Note that these two conversions are not the same operation and do not cancel: L/(1−L) always exceeds L, and L/(1+L) is always below it. Confusing them is how a batch ends up a percentage point away from where the maker thought it was.
The wax's maximum load is quoted on a wax basis on essentially every data sheet, so that is the basis the calculator checks against. It is a real physical limit, not a marketing number: wax holds only so much oil in solution, and beyond that the excess migrates to the surface as the candle cools and sits there as a wet film. That is why a load that looked fine at the pour can appear as sweating a week later.
Worked example: a 5 lb batch at 8% into twelve vessels
You are making twelve candles from 5 lb of a soy container wax whose data sheet gives a 10% maximum load. The fragrance is quoted at 8% and your supplier, like most, means 8% of the wax. The oil costs $2.25 per ounce by weight.
- Wax in ounces. 5 lb × 16 = 80 oz.
- Fragrance oil. 80 × 0.08 = 6.40 oz.
- In grams. 6.40 × 28.349523 = 181.44 g.
- Per pound of wax. 16 × 0.08 = 1.28 oz per lb.
- Total pour weight. 80 + 6.40 = 86.40 oz.
- The same load on a total basis. 6.40 ÷ 86.40 = 7.407%. If a supplier quotes you "7.4%" they may be describing this identical batch.
- Per candle. 86.40 ÷ 12 = 7.20 oz of finished wax per vessel, made up of 80 ÷ 12 = 6.667 oz of wax and 6.40 ÷ 12 = 0.533 oz of oil.
- Fragrance cost. 0.533 × $2.25 = $1.20 per candle, and 6.40 × $2.25 = $14.40 for the batch.
At 8% against a 10% ceiling this batch has real headroom. Had the same recipe been read on a total basis it would have needed 80 × 0.08 ÷ 0.92 = 6.957 oz, which is 8.696% of the wax — still legal against a 10% ceiling, but nearly a percentage point higher than intended, and the maker would have had no idea they had moved.
Choosing a load, and what it does and does not buy you
More oil is not linearly more scent. Fragrance in a candle has to dissolve into the wax, survive the pour, and then vaporise from the melt pool at the temperature a flame maintains. Beyond the point where the wax stops holding the oil in solution, additional oil does not throw better — it separates, it can affect how the wick burns, and it leaves a film on the surface.
So the ceiling on the data sheet is the number that matters, and this calculator treats it as a hard limit. Above it you get an error, and within ten percent of it a warning to pour a single test candle and leave it a week before committing the batch. Sweating is a slow fault: it appears after the candle has fully set and cooled, not at the pour.
Below the ceiling, the load you choose is a judgement about the oil, the wax and the vessel. Strong oils throw well at low loads; weak ones do not improve much at high ones. The only reliable way to settle it is to pour the same wax and wick at two or three loads, cure them for the same time, and burn them in the same room. Keep the wax, wick and vessel constant while you vary the load, or the test tells you nothing.
Cost scales exactly with load, and fragrance is usually the most expensive ingredient in a candle by a wide margin. On the worked example, $1.20 of the candle's material cost is fragrance — typically more than the wax, the vessel and the wick together on a small candle. Dropping from 8% to 6% cuts that to $0.90, a 25% saving on the single largest input. That is worth testing before you assume the higher load is doing anything.
Fragrance oil per pound of wax, both bases
| Load (% of wax) | Oil per lb of wax (oz) | Oil per 454 g of wax (g) | Same load as % of total |
|---|---|---|---|
| 3% | 0.48 | 13.61 | 2.913% |
| 4% | 0.64 | 18.14 | 3.846% |
| 5% | 0.80 | 22.68 | 4.762% |
| 6% | 0.96 | 27.22 | 5.660% |
| 7% | 1.12 | 31.75 | 6.542% |
| 8% | 1.28 | 36.29 | 7.407% |
| 9% | 1.44 | 40.82 | 8.257% |
| 10% | 1.60 | 45.36 | 9.091% |
| 12% | 1.92 | 54.43 | 10.714% |
Ounces per pound is 16 × L, grams per 454 g of wax is 453.59 × L, and the total-basis figure is L ÷ (1 + L). Read the last column whenever a supplier's percentage looks lower than you expected.
IFRA limits are a separate ceiling from the wax's
Two different maximums apply to a candle, and passing one does not mean passing the other. The wax maximum is a physical solubility limit from the wax manufacturer, and it is what this calculator checks. The IFRA Standards set maximum usage levels for individual fragrance materials by product category, on safety grounds, and they are enforced through the IFRA certificate of conformity your fragrance supplier should provide for each oil. That certificate names a maximum usage percentage for the category your product falls in, and it can be well below the wax's ceiling for oils containing restricted materials. Check both, take the lower, and keep the certificate on file — for anyone selling candles it is the document a regulator will ask for.
Mistakes that change what actually goes in the pot
- Measuring oil by volume. Fragrance oils vary in density, so a fluid ounce is not an ounce by weight and the error differs from oil to oil. Weigh everything.
- Reading the supplier's percentage on the wrong basis. A total-basis 8% is a wax-basis 8.696%. That is enough to cross a wax ceiling you thought you were under.
- Adding fragrance at the wrong temperature. Every wax data sheet names a temperature range for adding fragrance so it dissolves fully into the melt. Adding too cool leaves it poorly bound; adding too hot flashes off some of the more volatile components.
- Comparing loads across different waxes. Ceilings differ substantially between paraffin, soy and coconut blends, and so does how each holds oil below the ceiling. A load that works in one wax is not evidence about another.
- Changing load and wick together. Fragrance affects how the wax burns, so testing a new load with a new wick tells you nothing about either. Change one at a time.
- Judging throw before the cure. Container candles need time for the fragrance to bind through the wax. Burn the tests after the same cure period, or you are measuring cure time rather than load.
Where fragrance load sits in the rest of the recipe
Fragrance load is the last of three sizing decisions and depends on the first two. Start with the vessel: how much wax does it hold, and how many candles does a batch make? The candle wax calculator converts vessel volume into wax weight, which is the input this page starts from. Then choose the wax and read its ceiling. Only then pick a load.
The per-candle figures here feed straight into costing. Fragrance is usually the largest single material cost in a small candle, so the cost per candle output is the number to watch when you are pricing — and it is the one that moves most when you change a recipe.
The same percentage-basis trap appears across this whole category of craft. Soap makers express fragrance as a percentage of oils, which is a wax-basis equivalent, and size batches to a mould with the soap mould volume calculator. Resin casters mix by a fixed ratio rather than a percentage, sized with the resin mould volume calculator and the silicone mould material calculator, and coaters work in coverage per unit area with the epoxy coverage calculator. In every case the first question to ask of a percentage is what it is a percentage of.