What Superfat Percentage Should I Use? A Chart by Soap Type
Soap chemistry · Superfat · Updated 2026-07-22
Superfat is the percentage of oil in your recipe that you deliberately leave unsaponified, achieved by using slightly less lye than the oils could consume. Most cold-process makers work between 5 and 8 percent, with 5 percent the near-universal default; salt bars and 100 percent coconut bars go much higher, and liquid soap and laundry soap go much lower.
The number does two unrelated jobs at once, which is why the advice you find is contradictory. It is a skin-feel dial, and it is a safety margin that guarantees no free lye survives your scale's rounding error. This guide separates the two, then gives the by-type chart.
What superfat actually is
A lye calculator first works out how much sodium hydroxide would fully saponify your oils, using each oil's saponification value. Superfat then reduces that lye figure by your chosen percentage. At 5 percent superfat the calculator hands you 95 percent of the theoretical lye, so roughly 5 percent of your fat has no lye to react with and stays in the bar as free oil. You will also see this called a lye discount - same arithmetic, described from the other side.
The safety half matters more than makers give it credit for. Published SAP values are averages, not constants: the same oil varies by crop, region and refining, and different reference tables disagree in the third decimal place. Add a kitchen scale that rounds to the nearest gram and a lye that has absorbed atmospheric moisture, and a nominally exact recipe can drift lye-heavy. Classic Bells, DeeAnna Weed's long-running soap chemistry reference, puts the pure safety margin at roughly 1 to 3 percent - anything above that is a deliberate choice about how the bar feels, not insurance.
Superfat percentage chart by soap type
| Soap type | Commonly used superfat | Why | Trade-off you accept |
|---|---|---|---|
| All-purpose bar | 5% | The default for a balanced blend of hard fat, coconut and olive. Enough margin for SAP variation, little enough to keep lather crisp. | None worth naming. This is the band recipes are written for. |
| Facial bar | 3% to 8% | Sources split hard here. Some argue low, so the bar rinses clean off skin that is already oily; others argue high, for sensitive or mature skin. | Low can read as tight and stripping; high can leave a film that defeats the point of a face wash. |
| Moisturizing body bar | 8% to 10% | Free oil is the cheapest way to soften an otherwise cleansing recipe without reformulating it. | Softer bar, shorter life in the dish, measurably less lather. |
| Shampoo bar | 5% to 10% | Hair needs the sebum stripped less aggressively than skin, but excess free oil is what makes bars read as waxy on hair. | Above about 10% many people report dull, weighed-down hair - though hard-water scum is often the real culprit. |
| Salt bar | 15% to 20% | Salt bars are usually 70% or more coconut oil, which is aggressively cleansing. The high superfat is a correction, not a luxury. | Very little lather by design, and a long cure. Expect a dense, lotion-like bar rather than a foamy one. |
| 100% coconut bar | 15% to 20% | Coconut alone is harsh enough to be uncomfortable at 5%. Bramble Berry's Soap Queen recommends 20% for pure coconut bars. | Even at 20% it is a strong cleanser. Better suited to hands, laundry and salt bars than to a daily body bar. |
| Castile (100% olive) | 2% to 5% | Olive is already the mildest common oil. Extra free oil buys nothing and slows an already slow bar. | Nothing gained by going higher - just a softer bar and a longer wait. |
| Laundry soap | 0% to 2% | You want every fatty acid converted to soap. Free oil does not clean, and it can deposit on fabric. | Zero conditioning value, which is the point. Do not use these bars on skin. |
| Liquid soap (KOH) | 0% to 3% | Excess oil is the main cause of cloudy, separating liquid soap. Many makers finish at neutral and add any conditioning oil after dilution. | Clarity versus skin feel. Superfatting after dilution keeps both, at the cost of an extra step. |
| Shaving soap | 2% to 5% | Shaving soap is judged almost entirely on lather stability under a brush, and free oil is what collapses a lather. | A firmer, more cleansing puck. Conditioning usually comes from the recipe's stearic and glycerin, not from superfat. |
The facial bar row is the honest one. Soap Legacy's chart puts facial bars at 3 percent; Simple Life Mom puts them at 10 to 15 percent. Both are experienced makers writing about the same product. That is your signal that the by-type numbers are conventions, and the only way to settle it for your skin and your water is to pour two small batches and use them.
What each level of superfat actually costs you
| Superfat | Lather | Hardness / bar life | Rancidity (DOS) risk | Cure behaviour |
|---|---|---|---|---|
| 0% to 2% | Fullest and fastest | Hardest, longest-lasting | Lowest, all else equal | Normal, but zero margin for SAP error or scale rounding |
| 3% to 5% | Full | Firm | Low | Normal. Zap-test at 24 to 48 hours as usual |
| 6% to 8% | Slightly reduced | Slightly softer | Low to moderate | Normal. Most recipes sit here comfortably |
| 9% to 12% | Noticeably reduced, slower to build | Softer, dissolves faster in the dish | Moderate, and rising with polyunsaturated oils | Benefits from a longer cure to firm up |
| 13% to 20% | Minimal, can feel greasy | Soft unless the recipe is very hard-fat heavy | Highest, especially with soft oils | Reserve for salt bars and high-coconut recipes that need the correction |
A worked example: what three percentage points is worth
Take a 1,000 g oil batch at 60 percent olive, 25 percent coconut, 15 percent castor. Using the commonly published NaOH saponification values (olive 0.1353, coconut 0.1831, castor 0.1286 - these vary by source), the full-saponification lye is 81.18 + 45.78 + 19.29 = 146.25 g NaOH.
- 0% superfat: 146.25 g NaOH. No margin at all.
- 5% superfat: 146.25 x 0.95 = 138.94 g NaOH, leaving about 50 g of oil unsaponified.
- 8% superfat: 146.25 x 0.92 = 134.55 g NaOH, leaving about 80 g unsaponified.
The gap between 5 and 8 percent is 4.39 g of lye on a kilogram of oils. That is a meaningful skin-feel difference and it is also, uncomfortably, within reach of a cheap 1 g-resolution kitchen scale plus SAP variation between reference tables. It is the clearest argument for owning a 0.1 g scale and for never running a recipe at 0 percent.
Move the dial and watch the bar change. Soap Calculator puts superfat on a 0 to 15 percent control and recalculates the lye weight live against verified saponification values for 202 oils, NaOH for solid bars and KOH for liquid soap. The predicted bar properties - hardness, cleansing, conditioning, bubbly, creamy, iodine and INS - update as you move it, so you can see the lather and hardness cost of every extra point before you commit any oil. Download Soap Calculator: Lye & Recipe on the App Store.
How to choose your number
- Start from the recipe, not the chart: Superfat is a correction. If your recipe is 40 percent coconut, the honest fix is less coconut, not more free oil. Check the cleansing number first.
- Default to 5 percent: For any conventional blend of hard fat, coconut and a liquid oil, 5 percent is the number recipes are written and tested at. Deviate only with a reason.
- Test three bars, not three theories: Pour the same recipe at 2, 5 and 8 percent, cure them together, label them, and use them for a month. This settles the argument permanently for your skin and water.
- Raise it only for genuinely harsh recipes: Salt bars and high-coconut bars are the real cases for 15 percent and up. Everything else is preference, and preference above 10 percent costs you lather.
- Never go below about 2 percent: Below that you are relying on your scale and your SAP table being perfect. Zap-test regardless, but keep the margin.
Doing it in Soap Calculator
Set your oils, set superfat anywhere from 0 to 15 percent, and Soap Calculator returns the lye weight, water weight and total fat weight together, with the predicted bar properties and a fatty-acid blend ribbon underneath. Because the ribbon and the seven property scores redraw as you adjust an oil percentage, you can see immediately whether a high superfat is fixing a genuinely harsh blend or just papering over too much coconut. Every lye prompt renders in safety red, and the whole calculator runs on-device with no account. See Soap Calculator.
Frequently asked questions
What is superfat in soap making?
Superfat is the percentage of oil you leave unsaponified by using slightly less lye than your oils could react with. At 5 percent superfat the calculator gives you 95 percent of the full lye amount, so about 5 percent of the fat stays in the finished bar as free oil. It is also called a lye discount.
Is 10 percent superfat too much?
Not unsafe, but it has costs. At 10 percent you will notice reduced lather, a softer bar that dissolves faster, and a greater tendency toward rancidity if your recipe leans on polyunsaturated oils like sunflower, soybean or hemp. For a hard-fat-heavy recipe on dry skin, 10 percent is reasonable. For a general body bar, 5 to 8 percent gets you most of the benefit with none of the drawbacks.
What superfat should I use for a shampoo bar?
Most makers land between 5 and 10 percent. Published advice ranges from 2 percent up to 12, and the disagreement is real. Above roughly 10 percent, hair commonly reads as dull or weighed down - though if you have hard water, the film is usually calcium and magnesium soap scum rather than your superfat, and an acidic rinse fixes it faster than dropping the dial.
Does superfat make soap safer to use?
Partly. A margin of roughly 1 to 3 percent covers the realistic error in published SAP values, scale rounding and moisture in your lye, so no free alkali survives. Beyond that, extra superfat is about skin feel, not safety. It is not a substitute for accurate weighing or for zap-testing the finished bar.