Soap Batch Scaler Calculator
Scale any soap recipe up or down by weight.
Enter your original recipe and target batch size to get proportional ingredient amounts.
How soap recipe scaling works:
Soap recipes are proportional — every ingredient must scale by the same factor. If you double the oils, you must double the lye and water too. Getting this wrong means your soap will be lye-heavy (caustic and unsafe) or oil-heavy (soft and rancid).
Scaling formula:
Scale factor = New batch size / Original batch size
New ingredient amount = Original amount × Scale factor
Important: Scale factor applies to ALL ingredients — oils, lye, water, fragrance, colorant, and additives.
Worked example:
Original recipe makes 2 lbs:
- Olive oil: 10 oz
- Coconut oil: 6 oz
- Lye (NaOH): 4.2 oz
- Water: 6 oz
You want 5 lbs. Scale factor = 5 / 2 = 2.5×
- Olive oil: 10 × 2.5 = 25 oz
- Coconut oil: 6 × 2.5 = 15 oz
- Lye: 4.2 × 2.5 = 10.5 oz
- Water: 6 × 2.5 = 15 oz
Mold capacity check:
Before scaling up, make sure your mold can hold the new volume. Soap weighs approximately 9–10 oz per inch of height in a standard loaf mold (3.5 × 9 inches).
Tips for scaling:
- Always weigh in the same unit (oz or grams) — never mix
- Small batches (under 1 lb total oils) are harder to work with because trace happens fast
- Large batches (over 5 lbs) generate more heat — use lower temperatures to avoid gel cracking
- Fragrance load stays proportional: if the original uses 3% fragrance by oil weight, the scaled version uses the same 3%
- When scaling down, round lye DOWN (safer to have slightly more oil than too much lye)
- When scaling up, consider splitting into two batches if you are new — large batches leave no room for error
Superfat does not change: A 5% superfat recipe stays 5% regardless of batch size, because the lye amount was already calculated to leave 5% of the oil unsaponified.