Flaxseed (linseed) oil: SAP value and fatty acids
Flaxseed (linseed) oil has a saponification value of 191 mg KOH/g. One gram needs 0.136 g of sodium hydroxide (NaOH) for bar soap or 0.191 g of potassium hydroxide (KOH) for liquid soap to turn fully into soap, before any superfat.
Key numbers
- SAP, NaOH
- 0.136161 g per g oil
- SAP, KOH
- 0.191 g per g oil
- Saponification value
- 191 mg KOH/g
- INCI name
- Linum Usitatissimum Seed Oil
Example: 100 g of Flaxseed (linseed) oil with no superfat needs 13.6 g of 100% NaOH, or 19.1 g of 100% KOH. A 5% superfat uses 5% less.
In soap
Its main fatty acids in our cited profile are linolenic (56%) and oleic (19.2%). The eight fatty acids used in soap-quality scores make up 99.2% of the profile.
On its own it scores 9 for hardness, 0 for cleansing and 90 for conditioning, with a saturated : unsaturated split of 9 : 90.
Very high in linolenic acid, so it oxidizes fast and is prone to dreaded orange spots in soap.
Fatty-acid profile
| Fatty acid | % of fatty acids | Counts toward |
|---|---|---|
| lauric | 0% | hardness, cleansing, bubbly lather |
| myristic | 0.1% | hardness, cleansing, bubbly lather |
| palmitic | 5.4% | hardness, creamy lather |
| stearic | 3.5% | hardness, creamy lather |
| ricinoleic | 0% | conditioning, bubbly and creamy lather |
| oleic | 19.2% | conditioning |
| linoleic | 15% | conditioning |
| linolenic | 56% | conditioning |
Basis: USDA FDC SR Legacy 167702 (cold-pressed flaxseed oil), converted to % of total fatty acids.
Soap-quality scores (this oil alone)
| Hardness | 9 |
|---|---|
| Cleansing | 0 |
| Conditioning | 90 |
| Bubbly lather | 0 |
| Creamy lather | 9 |
Each score adds up certain fatty acids, the way Soap Ledger scores a whole recipe. They are for comparing recipes; they don't predict how a bar will feel, and they say nothing about safety or skin.
Sources
SAP value: 191 mg KOH/g (Median of sources), from Dash B. et al. (2026) Cold pressed oils: a systematic review on physicochemical properties, nutritional composition and pharmacological activities. Frontiers in Nutrition. doi:10.3389/fnut.2026.1747029, Frontiers (open access, peer-reviewed review). Printed value: 188–195 mg KOH/g.
Published values we checked:
- 186 - 196 mg KOH/g — From Nature With Love (soap/cosmetic supplier)
- NaOH 0.1358 / KOH 0.1913 g alkali per g oil — Certified Lye
- 188–195 mg KOH/g — Frontiers (open access, peer-reviewed review)
Fatty acids: USDA FoodData Central, SR Legacy: Oil, flaxseed, cold pressed (FDC ID 167702), U.S. Department of Agriculture, Agricultural Research Service. Also checked: MDPI (Table 2 (Linseed Oil)).
NaOH and KOH values are converted from mg KOH/g with the molar masses 39.997 and 56.106 and rounded to 6 decimals, exactly as in the Soap Ledger app. Real oils vary by origin, grade and lot: check your supplier's certificate of analysis. Verify every weight before you make this, and follow lye safety. Not a safety or compliance certification.
Last updated .