Melt and pour soap calculator
How much base your mould takes, how much fragrance it will actually hold, and the temperatures to work at. No lye, no superfat and no cure — melt and pour base arrives as finished soap.
INPUTS
Working from
No lye, no superfat and no cure — the base was made into soap before it reached you. The weight you melt is the weight of soap you end up with.
g
3.5 oz. No cure, so this is also the mould fill.
Your base
The transparent one. Shows colour cleanly and sweats the most — wrap it the moment it is firm. Holds up to about 3% fragrance.
Scent
Scenting with
% of base
1–3% for fragrance oil, less for essential — well under the 3–6% a cold process bar takes. Your own scent's IFRA category 9 maximum is the number that binds.
Extras
Colour it
Mica or pigment at about 0.15 g per 100 g of base for a solid colour.
Dry additive
No lye here, which is why melt and pour is the one soap you can safely make with children — but it is still molten liquid at 55°C (131°F) and it sticks to skin. Melt in short bursts and stir between them; past 65°C (149°F) the base scorches, yellows and will not set firm again.
RESULTS
Base to melt
1200.0 g
2.65 lb 12 bars at 100 g
Fragrance oil at 2%
24.0 g
2.0g per bar ceiling 3%
Everything into the jug
| Ingredient | Rate | Weight |
|---|---|---|
| Clear glycerin base | — | 1200.0 g |
| Fragrance oil | 2% | 24.0 g |
| Mica or pigment | 0.15 g/100 g | 1.8 g |
| Total | — | 1225.8 g |
Temperatures and timing
| Step | Celsius | Fahrenheit |
|---|---|---|
| Melt to | 55°C | 131°F |
| Add scent and colour under | 60°C | 140°F |
| Never exceed | 65°C | 149°F |
| Set at room temperature | 4 hours | |
| Set in the fridge | 60 minutes | |
Mould space needed
1165 ml
Usable after
4 hours
No cure. The base was already soap when you bought it, so the bar is ready as soon as it is solid — and it does not shed water the way a cold process bar does. That also means it never hardens further: wrap each bar as soon as it is firm, or the glycerin will pull moisture out of the air and bead on the surface.
Print the safety checklist
Lye handling, kit and the order of operations, on one page you can pin up where you work. Free.
Get your free download
Soap Making Safety Checklist
How this is worked out
Melt and pour is the one soap on this site that involves no chemistry on your part. The base arrives already saponified, so the calculation is simply how much of it a mould takes and what percentage of that weight everything else should be. Two things differ from every other tool here. There is no cure, so no weight is lost — the base you melt is the soap you get, and bar count is base weight divided by bar weight with nothing taken off. And the fragrance ceiling is far lower: 1–3% rather than the 3–6% a cold process bar absorbs, because finished soap has nothing left to bind surplus oil with. Softer bases are lower still — shea butter tops out around 2.5%, since the butter or milk in it has already softened the bar before the fragrance gets a chance to.
base for N bars = bars × bar weight (no cure loss — none applies)
base for a mould = mould ml × 1.03
fragrance = base weight × usage rate
ceiling = lower of the base’s limit and your scent’s IFRA category 9 figure
Questions makers ask
How much fragrance oil for melt and pour soap?
1–3% of the base weight, with 2% the working default — noticeably less than cold process. On 1200 g of base that is 24 g, or about 2.0 g in each of 12 bars. Per pound of base, 2% works out to roughly 9.1 g — about 0.32 oz.
Why does melt and pour take less fragrance than cold process?
Because there is nothing left to react with it. A cold process bar is still saponifying and can absorb 3–6% — on the same batch that would be 36 g. Melt and pour base is finished soap, so surplus oil has nowhere to go: it sweats out, keeps the bar tacky, or stops it setting firm at all.
Do I need a lye calculator for melt and pour?
No, and that is the point of melt and pour. The manufacturer already did the saponification — you are melting and colouring soap that is finished. There is no lye to weigh, no superfat to choose and no water discount. If you want that control, cold process is the next step up.
How long does melt and pour soap take to cure?
It does not cure. The bar is usable as soon as it is solid — about 4 hours at room temperature or 60 minutes in the fridge, against 28 days for cold process. It also does not lose water over time, so the base you weigh is the soap you end up with.
What temperature should I melt the base to?
Around 55°C (131°F), and never past 65°C (149°F) — scorched base yellows, smells burnt and will not set firm again. Add fragrance and colour below 60°C (140°F) or the scent goes off with the steam.
Why is my melt and pour soap sweating?
Glycerin pulls moisture out of the air, and melt and pour base is full of it. Beads on the surface are almost always humidity rather than a mistake. Wrap each bar in cling film the moment it is firm, use a low-sweat base if your room is damp, and keep the fragrance rate down — over-scenting makes it much worse.
How much base does my mould take?
Multiply the internal volume in millilitres by 1.03 — melted base is slightly denser than water. A 10 in silicone loaf holds about 2007 ml, so roughly 2068 g of base, which cuts into about 20 bars at 100 g.
Can I add oats or clay to melt and pour?
Yes, at around 2 g per 100 g of base. Heavy additives sink while the bar sets, so let the base thicken slightly and stir again before pouring. Adding oils or butters is a different matter — extra oil softens finished soap and it will not firm back up.
Can I use essential oils instead?
Yes, usually at a lower rate — 1.5% is a sensible default. Some essential oils are restricted well below fragrance-oil rates, and a few will discolour a clear base. The maximum on your own supplier's IFRA certificate is the figure that binds.
Read before your next batch
- How to use a soap calculator What every field means, where the number comes from, and how to tell when a result is wrong before you have mixed anything.
- What is superfat in soap making? The oil left deliberately unsaponified in a bar — what it is for, what each setting changes, and why the number matters more as a safety margin than as a skin treatment.
- Cold process vs hot process soap Same oils, same lye, two very different afternoons — and one difference that decides it for most people.
- Water discounts explained Lye concentration, water-to-lye ratio and per cent of oils are three names for one decision — and the decision has nothing to do with how much lye you need.