Lye Calculator for Multiple Oils
A blended recipe has to be worked oil by oil and then added up, because the SAP value belongs to the oil and not to soap in general — take each figure from that oil's own data, whether a supplier sheet or a standard SAP table. Olive at 300 g (SAP 190), coconut at 150 g (SAP 258) and castor at 50 g (SAP 180) give 300×190 + 150×258 + 50×180 = 104,700, which divided by 1402.5 is 74.7 g of NaOH, and taking off 5% superfat leaves 70.9 g. The blend SAP shown alongside, 209.4 here, is the weighted average: it is the number to use if you later treat this blend as a single oil. Swap one oil and the blend SAP moves, so the lye has to be redone.
Your numbers
Lye needed
70.9g
Blend SAP value
209.4
Water
142g
Batter total
713g
Formula
Lye needed = (Oil 1 weight × Oil 1 SAP value + Oil 2 weight × Oil 2 SAP value + Oil 3 weight × Oil 3 SAP value) ÷ 1402.5 × (1 − Superfat ÷ 100)
Lye goes into the water, never water into the lye — the wrong order can boil up and spit in seconds. Wear goggles and gloves, and mix in stainless steel or HDPE, never aluminium, which lye attacks and releases hydrogen from. The solution heats itself to 80–90°C on contact, so no glass and no thin plastic. One mistyped oil weight throws the lye off: too little leaves a soft bar that never firms, too much leaves a caustic one. Set an unused oil's weight to zero — a leftover SAP value on its own changes nothing.
What to enter
| Input | Default | Accepted range |
|---|---|---|
| Oil 1 weight (g)Weight of the first oil alone, excluding water and lye. | 300 | 0 and up |
| Oil 1 SAP valueThat oil's SAP — milligrams of KOH per gram, taken from its own data sheet. | 190 | 0 ~ 300 |
| Oil 2 weight (g)Weight of the second oil; leave it at zero if unused. | 150 | 0 and up |
| Oil 2 SAP valueThe second oil's SAP value — coconut near 258, palm near 199. | 258 | 0 ~ 300 |
| Oil 3 weight (g)Weight of the third oil — the slot for small additions such as castor. | 50 | 0 and up |
| Oil 3 SAP valueThe third oil's SAP value — castor near 180, shea butter near 128. | 180 | 0 ~ 300 |
| Superfat (%)Oil left unsaponified; the lye is cut by this much. | 5 | 0 ~ 20 |
Step by step
Quick reference table
Results when only Oil 1 weight (g) changes and everything else stays put.
| Oil 1 weight (g) | Lye needed (g) | Blend SAP value | Water (g) |
|---|---|---|---|
| 150 | 51.6 | 217.7 | 103 |
| 225 | 61.3 | 212.8 | 123 |
| 300 | 70.9 | 209.4 | 142 |
| 450 | 90.2 | 204.9 | 180 |
| 600 | 109.5 | 202.1 | 219 |
What each result means
| Result | At default values |
|---|---|
| Lye needed (g)Lye needed; too little leaves it soft, too much leaves it caustic. | 70.9 |
| Blend SAP valueThe blend's SAP, weighted by oil weight — it moves if any one oil changes. | 209.4 |
| Water (g)Water to dissolve in; lye goes into water, never the reverse. | 142 |
| Batter total (g)Oils, water and lye together. | 713 |
Common mistakes
Lye goes into the water, never water into the lye — the wrong order can boil up and spit in seconds. Wear goggles and gloves, and mix in stainless steel or HDPE, never aluminium, which lye attacks and releases hydrogen from. The solution heats itself to 80–90°C on contact, so no glass and no thin plastic. One mistyped oil weight throws the lye off: too little leaves a soft bar that never firms, too much leaves a caustic one. Set an unused oil's weight to zero — a leftover SAP value on its own changes nothing.
Glossary
- Oil 1 weight
- Weight of the first oil alone, excluding water and lye.
- Oil 1 SAP value
- That oil's SAP — milligrams of KOH per gram, taken from its own data sheet.
- Oil 2 weight
- Weight of the second oil; leave it at zero if unused.
- Oil 2 SAP value
- The second oil's SAP value — coconut near 258, palm near 199.
- Oil 3 weight
- Weight of the third oil — the slot for small additions such as castor.
- Oil 3 SAP value
- The third oil's SAP value — castor near 180, shea butter near 128.
- Superfat
- Oil left unsaponified; the lye is cut by this much.
- Lye needed
- Lye needed; too little leaves it soft, too much leaves it caustic.
- Blend SAP value
- The blend's SAP, weighted by oil weight — it moves if any one oil changes.
- Water
- Water to dissolve in; lye goes into water, never the reverse.
- Batter total
- Oils, water and lye together.
Frequently asked questions
Q. How is Lye Calculator for Multiple Oils calculated?
Lye needed = (Oil 1 weight × Oil 1 SAP value + Oil 2 weight × Oil 2 SAP value + Oil 3 weight × Oil 3 SAP value) ÷ 1402.5 × (1 − Superfat ÷ 100) — A blended recipe has to be worked oil by oil and then added up, because the SAP value belongs to the oil and not to soap in general — take each figure from that oil's own data, whether a supplier sheet or a standard SAP table. Olive at 300 g (SAP 190), coconut at 150 g (SAP 258) and castor at 50 g (SAP 180) give 300×190 + 150×258 + 50×180 = 104,700, which divided by 1402.5 is 74.7 g of NaOH, and taking off 5% superfat leaves 70.9 g. The blend SAP shown alongside, 209.4 here, is the weighted average: it is the number to use if you later treat this blend as a single oil. Swap one oil and the blend SAP moves, so the lye has to be redone.
Q. Can you walk through an example?
With Oil 1 weight 300g, Oil 1 SAP value 190, Oil 2 weight 150g, Oil 2 SAP value 258, Oil 3 weight 50g, Oil 3 SAP value 180, Superfat 5%, the answer is Lye needed 70.9g.
Q. What do I need to enter?
Enter Oil 1 weight, Oil 1 SAP value, Oil 2 weight, Oil 2 SAP value, Oil 3 weight, Oil 3 SAP value, Superfat. The result recalculates as you type, and an empty box counts as zero.
Q. How much does the answer move if I change a number?
Changing only Oil 1 weight (g) moves the answer to Oil 1 weight (g) 150 → Lye needed (g) 51.6 and Oil 1 weight (g) 600 → Lye needed (g) 109.5. The table below lays out five steps.
Q. How are the numbers rounded?
Money is shown to the nearest whole unit, percentages to one decimal place and everything else to two. What you see is rounded; the calculation itself carries the unrounded value forward.
Q. Anything to watch out for?
Lye goes into the water, never water into the lye — the wrong order can boil up and spit in seconds. Wear goggles and gloves, and mix in stainless steel or HDPE, never aluminium, which lye attacks and releases hydrogen from. The solution heats itself to 80–90°C on contact, so no glass and no thin plastic. One mistyped oil weight throws the lye off: too little leaves a soft bar that never firms, too much leaves a caustic one. Set an unused oil's weight to zero — a leftover SAP value on its own changes nothing.
Related calculators
Materials differ in density and absorption. If your label states a figure, use it — the defaults here are only common values.