Candle Wax CalculatorParaffin Wax Calculator: Batch Amounts With Second-Pour Reserve
Paraffin is the classic candle wax — cheap, throws scent well, and burns bright. It also shrinks as it cools, which is why paraffin candles get a second pour and soy candles usually don't.
This paraffin wax calculator works out your batch wax, the 15% second-pour reserve (held back from the batch total), and the fragrance oil, using a typical paraffin density of 0.90 g/ml.
Paraffin wax calculator
Enter your container size and batch details to get the paraffin wax, second-pour reserve, and fragrance amounts for your batch.
How the paraffin batch formula works
Paraffin math runs on its density of 0.90 g/ml and its habit of shrinking as it cools. First, total volume = container volume × number of candles, then the safety margin is added on top (multiply by 1 + margin/100). That volume is converted to weight with the paraffin density: wax grams = volume ml × 0.90. That is the batch total — the total wax to buy, margin included.
Because paraffin contracts on cooling and leaves a sinkhole around the wick, a second pour is standard practice. The reserve is 15% of the batch total, held back from it — not extra on top. Pour the rest first, let it set completely, then melt the reserve for the second pour.
Fragrance is dosed on the wax weight before the margin: fragrance = un-margined wax × (load ÷ 100), split between the first pour and the reserve in the same 85/15 proportion so the scent stays even.
Limits: the 15% reserve is a common starting point (adjustable) — heavily additived blends can shrink a little more or less. Fragrance loads above the wax supplier's stated maximum are unsafe regardless of what the math allows. The 0.90 g/ml figure is a typical density used to convert the volume of the finished candle (to the fill line) into wax weight.
Paraffin density and the shrinkage problem
Paraffin has a typical density of about 0.90 g/ml — used to convert the volume of the finished candle (to the fill line) into wax weight. That single number converts any container volume into a wax weight for the scale.
The complication is cooling. Paraffin forms crystals as it solidifies, and the crystal structure takes up less space than the liquid did. The result is visible shrinkage: the wax pulls away from the glass and a sinkhole forms around the wick. This is normal paraffin behavior, not a mistake in your pour.
The standard fix is the second pour (sometimes called a repour). You deliberately hold back about 15% of the batch wax — part of the margined total, not extra — let the first pour cool and set completely, then melt the reserve and fill the sinkholes. The top sets smooth the second time because there is far less wax contracting at once.
Limitations of paraffin batch math
The 15% reserve is a common starting point (adjustable), but shrinkage varies with the exact paraffin blend, additives like vybar, and how fast the candles cool. Drafty, cold rooms increase shrinkage; a warm, still cooling area reduces it. If your sinkholes routinely swallow more than the reserve, slow the cooling before increasing the percentage.
Fragrance loads are bounded by safety, not arithmetic. The calculator offers up to 10%, but your wax supplier's maximum for your specific wax is the hard ceiling — exceeding it risks fragrance pooling on the surface and an unsafe burn.
Finally, this calculator sizes wax and fragrance only. Wicks, dye, and containers are separate decisions; size the wick from the container diameter with the wick calculator, and always burn-test the finished, fragranced candle.
Worked example: four 240 ml jars at 10% fragrance
Four containers at 240 ml each = 960 ml of wax. Add the 10% safety margin: 960 × 1.10 = 1056 ml. Convert to weight with the paraffin density: 1056 × 0.90 = 950.4 g of paraffin for the batch — the total to buy.
The second-pour reserve is 15% of that total, held back: 950.4 × 0.15 = 142.6 g. Pour 807.8 g first; let it set completely, then melt the reserve for the second pour.
Fragrance at 10% load is dosed on the un-margined wax weight: 864 × 0.10 = 86.4 g of fragrance oil. Split it with the wax — about 73.4 g in the first pour and 13 g in the reserve — so the scent stays even.
Weigh the fragrance separately — never guess it by volume, since fragrance oils vary in density.
Related calculators
- Gel Wax CalculatorFree gel wax calculator: batch gel wax weight and safe 0–5% fragrance loads.
- Soy Wax CalculatorFree soy wax calculator: enter container diameter, height, and candle count to get wax and fragrance oil amounts in grams, with a worked example.
- Candle Wick Size CalculatorFind the right wick size for your candle with this free wick size calculator.
The main wax calculator has links to every tool.
Frequently asked questions
Why does paraffin need a second pour?
Paraffin shrinks noticeably as it cools, pulling away from the container walls and leaving a crater or sinkhole around the wick. A second pour of reserved wax, done after the first pour has fully set, fills the shrinkage and gives a smooth top. Most paraffin candles need it; skipping it leaves a visibly sunken surface.
How much extra wax should I hold back for the second pour?
Hold back 15% of the batch's margined wax total — a common starting point (adjustable), not a fixed rule. Pour the remaining 85% first. Do not add the reserve's share of fragrance until the second pour, so the scent load stays consistent across both pours.
What fragrance load is safe for paraffin?
Container paraffin blends typically hold 6–10% fragrance by weight; the calculator offers 3, 6, 8 and 10%. The 3% option is for straight (unblended) paraffin, which holds only about 3% without additives. Never exceed the maximum your wax supplier states for your specific wax — overloading causes sweating, poor burning, and in extreme cases a fire risk.
What is paraffin's density?
About 0.90 g/ml — a typical density used to convert the volume of the finished candle (to the fill line) into wax weight. So a container that holds 100 ml to the fill line needs about 90 g of paraffin on the scale.
Can I use the second-pour reserve for the first pour instead?
No — the reserve exists because shrinkage is certain, not possible. Pouring it all at once just makes a deeper sinkhole. Melt the first-pour amount, let the candles cool completely (several hours), then melt the reserve and top up.
Does paraffin shrink more than soy wax?
Yes, noticeably. Soy wax also contracts a little, but paraffin's crystalline structure makes its shrinkage the most dramatic of the common candle waxes — which is why the second pour is a paraffin ritual rather than an occasional fix.
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