How much fragrance oil do I put in cold process soap?
The usual answer is 3–6% of the oil weight: 5% of 1,000 g of oils is 50 g of fragrance oil, which is 1.76 oz, or 0.80 oz per pound of oils. Five percent is a sensible default for a fragrance oil; three percent for a strong one or a light touch; six percent is heavy and, for many fragrances, past the supplier's limit. Essential oils run lower — 1–3% — both because they are more concentrated and because many have dermal limits well under a fragrance oil's.
| Load | Per 1,000 g oils | In ounces | oz per lb of oils | % of finished soap |
|---|---|---|---|---|
| 1% of oils | 10 g | 0.35 oz | 0.16 oz/lb | 0.7% |
| 2% of oils | 20 g | 0.71 oz | 0.32 oz/lb | 1.4% |
| 3% of oils | 30 g | 1.06 oz | 0.48 oz/lb | 2.1% |
| 4% of oils | 40 g | 1.41 oz | 0.64 oz/lb | 2.7% |
| 5% of oils | 50 g | 1.76 oz | 0.80 oz/lb | 3.4% |
| 6% of oils | 60 g | 2.12 oz | 0.96 oz/lb | 4.0% |
Finished soap = oils + lye + water at 33% lye concentration (1,424 g) + the fragrance. Computed by this site's engine; 2.20 lb of oils.
Supplier usage rates and IFRA maximums are written as a percentage of the finished product — the whole bar, water and lye included. Soapers state loads as a percentage of the oils. On an ordinary recipe the finished soap weighs about 1.42× the oils, so the two percentages differ by about a third: 5% of oils is only 3.4% of the finished soap, and a supplier's “max 5%” allows roughly 7.5% of oils. Most people get this backwards and under-scent, which is harmless; the dangerous mistake is the rare one where someone reads a 2% max as 2% of oils on a heavily discounted recipe and lands over it. Enter the supplier's number in the tool's IFRA max field and it does the conversion.
Reading the IFRA certificate
Every reputable fragrance oil comes with an IFRA conformity certificate listing a maximum percentage for each product category. Bar soap and hand soap are category 9 (rinse-off products with body and hand exposure); leave-on lotion is category 5; candles are 12. The category 9 number is the ceiling for that specific fragrance in soap — it can be 100% for a bland vanilla or under 2% for a cinnamon or citral-heavy blend. There is no universal “safe fragrance percent”; there is the number on the sheet for the oil in your hand. The table below turns a sheet value into the oil-percent you are used to:
| Max on the IFRA sheet (of finished soap) | Equivalent % of oils | Max grams per 1,000 g oils |
|---|---|---|
| 1% | 1.4% | 14 g |
| 2% | 2.9% | 29 g |
| 3% | 4.4% | 44 g |
| 4% | 5.9% | 59 g |
| 5% | 7.5% | 75 g |
Same batch assumptions as above. The conversion shifts with your water: a drier recipe (higher lye concentration) has less finished weight, so the same sheet percentage allows slightly less fragrance.
Essential oils in cold process soap
Essential oils are used at lower rates, partly for cost, mostly for skin: many carry dermal limits in the low single digits, and some — cinnamon, clove, citral-rich oils like lemongrass and litsea — are potent sensitizers with limits under 1%. They also behave differently in lye: citrus fades to almost nothing over cure, florals and mints hold, spices and clove can seize a batch in seconds. Customary starting points, to be checked against the supplier's IFRA sheet for the specific oil:
| Essential oil | Customary CP load (of oils) | Notes |
|---|---|---|
| Lavender | 2–3% | Sticks well; the reliable one. |
| Sweet orange, lemon, lime (cold-pressed) | 2–3% | Fades badly in CP; 5- or 10-fold orange holds better. |
| Peppermint, spearmint | 1.5–2.5% | Strong; cooling on skin above that. |
| Tea tree, eucalyptus, rosemary | 1.5–2.5% | Medicinal notes carry at modest loads. |
| Lemongrass, litsea (may chang) | 1–2% | Potent; citral is a sensitizer — check the IFRA sheet. |
| Patchouli, cedarwood, vetiver | 2–3% | Base notes; anchor citrus blends. |
| Cinnamon leaf, clove bud | ≤ 0.5% | Strong sensitizers; accelerate trace hard. Use as a trace note, not a load. |
Community norms for cold process, not limits; the IFRA certificate for your supplier's specific oil overrides this table.
Cold process batter reaches 150–180 °F (65–80 °C) in gel and stays alkaline for days; volatile top notes evaporate and some molecules are changed by the lye. Citrus essential oils and light fragrance oils lose the most. Loading heavier is the blunt fix and runs into the IFRA ceiling; the better fixes are anchoring citrus with a base note, choosing fragrances the supplier tested in CP, and adding the scent at thin trace rather than into the hot oils.
Ounces per pound, and the 1 oz PPO habit
US suppliers often say “use 1 oz per pound of oils” (PPO). One ounce per pound is 6.25% of oils — about as heavy as it is sensible to go with most fragrance oils, and above the limit for some. 0.5 oz PPO is 3.13%, a comfortable everyday load. The tool accepts oz per pound directly and shows the percent, so you can compare a supplier's PPO advice with the IFRA sheet instead of guessing.