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 first-pour wax, the 15% second-pour reserve, and the fragrance oil for the batch, using paraffin's real 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 liquid 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. This is the wax_total — the wax to melt for the first pour.
Because paraffin contracts on cooling and leaves a sinkhole around the wick, a second pour is standard practice. The reserve is 15% of the first-pour wax, held back and melted again after the candles set. Fragrance is then calculated as a percentage of the first-pour wax weight: fragrance grams = wax_total × fragrance_load/100.
Limits: the 15% reserve covers typical paraffin shrinkage; 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.
Paraffin density and the shrinkage problem
Melted paraffin has a density of about 0.90 g/ml — every 100 ml you pour weighs roughly 90 g on the scale. That single number converts any container volume into a wax weight.
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, 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.
Worked example: four 240 ml jars at 10% fragrance
Four containers at 240 ml each = 960 ml of liquid wax. Add the 10% safety margin: 960 × 1.10 = 1,056 ml. Convert to weight with the paraffin density: 1,056 × 0.90 = 950.4 g of paraffin for the first pour — call it 950 g on the scale.
The second-pour reserve is 15% of that: 950.4 × 0.15 = 142.6 g, about 143 g held back. Fragrance at 10% load is dosed on the un-margined wax weight: 864 × 0.10 = 86.4 g of fragrance oil, weighed into the first-pour wax (add about 14 g more to the reserve when you melt it, so the scent stays even).
Total wax to buy for the batch: 950 + 143 = 1,093 g, just under 2.5 lb. Weigh the fragrance separately — never guess it by volume, since fragrance oils vary in density.
Limitations of paraffin batch math
The 15% reserve is the industry standard, 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 12%, 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.
Related calculators
- Gel Wax CalculatorFree gel wax calculator: batch gel wax weight and safe 3–5% fragrance loads.
- Soy Wax CalculatorFree soy wax calculator: enter container diameter, height, and candle count to get exact 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?
15% of the first-pour wax is the standard reserve. It covers typical paraffin shrinkage with a little to spare. Hold it back unmelted or melted — either way, do not add fragrance to the reserve until the second pour, so the scent load stays consistent.
What fragrance load is safe for paraffin?
Most paraffin waxes safely hold 8–12% fragrance by weight; the calculator offers 8, 10, and 12%. 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 in the melted state. So 100 ml of melted paraffin weighs about 90 g. This calculator uses that figure to convert your container volume into the wax weight to put 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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