Melt and pour calculator – base, scent and colour to fill a mould

The melt and pour batch calculator works out how much soap base a mould needs to fill it, then the fragrance and colour to match, all from the mould volume and the loads you choose. Melt and pour skips lye and cure: you melt a ready-made base, stir in scent and colour, and pour. Because the base is close to the density of water, the grams you need land near the mould volume in cubic centimetres, and this tool turns that into base, fragrance and colorant weights in one step.

It is for soapers working with a melt and pour base who want a mould filled cleanly the first time, without a leftover puck or a half-empty cavity. The per-bar figures also show how much scent and colour each finished bar carries.

Melt and pour is forgiving on chemistry and fussy on heat and dose. Overheat the base and it turns rubbery; over-fragrance it and the bar sweats. The loads here keep both in the range that pours smooth and sets clear.

✂️ How to use the melt and pour calculator

Start with the mould volume. Enter it in cubic centimetres, which you can measure by filling the mould with water and weighing it, since a gram of water is a cubic centimetre. A 500 cm3 mould is a common small loaf.

Choose the base type. A clear glycerin base, a white base, and enriched bases like shea or goat milk pour and look different, and the type guides the fragrance and colour that suit it. Clear is the default and the most versatile.

Set the fragrance load as a percentage of the base weight. Two percent is a reliable rate for melt and pour, which holds less scent than cold process. The field runs from about 1 to 3 percent.

Add fragrance once the melted base has cooled to about 60 degrees Celsius, not while it is piping hot. Fragrance stirred into near-boiling base flashes off, so a bar that smelled strong in the pot can end up faint on the shelf.

Pick the colour intensity next. Melt and pour takes colour easily, especially the clear base, so pastel, medium and bold map to smaller doses than a cold process bar would need. Choose none if you want a natural, uncoloured bar.

Read the results from the top. The hero number is the base to melt; below it sit the fragrance grams, the colorant amount and the bar yield. Melt the base, cool it, then stir in colour and scent before pouring.

Calculator fields explained

Mould volume (cm3) – the internal space to fill, measured directly or by weighing water poured into the mould. There is no default; it comes from your mould. The base weight scales straight from this.

Base type – clear, white, shea, goat milk or similar. Default is clear. The type sets a small density adjustment and guides which fragrance and colour loads suit the base.

Fragrance load (percent of base) – how much scent to add, as a share of base weight. Default is 2, with a working range of 1 to 3. Melt and pour holds less than cold process, so the ceiling is lower.

Colour intensity – none, pastel, medium or bold, mapping to a colorant rate. Default is medium. Clear base especially reads colour strongly, so the doses are smaller than for an opaque bar.

Number of bars – how many bars the mould makes, used for the per-bar figures. Default is 5. It does not change the batch totals.

📊 Understanding the results

The base figure is what you weigh and melt. A 500 cm3 mould takes about 500 g of base, because melt and pour soap sits close to the density of water. A 500 cm3 mould takes about 500 g of melt and pour base. That near-equality makes the base easy to estimate from any mould you can measure.

Fragrance comes out lower than a cold process soaper expects. At 2 percent of a 500 g base that is 10 g, and pushing much past 3 percent does not make the bar smell stronger, it makes it weep. The base simply cannot bind as much scent.

Colour in melt and pour is a light touch. The same shade that needs a full teaspoon of mica in an opaque cold process bar reads strongly in clear base at a fraction of that, so the doses here are smaller and easy to overshoot.

Fragrance and colour are dosed on the base weight, since melt and pour has no separate oils. Over-fragrancing is the most common fault: above about 3 percent the excess oil beads on the surface as sweat, and no amount of curing fixes it because melt and pour does not cure.

The per-bar figures ground the batch. Ten grams of fragrance across 5 bars is 2 g each, a clear but not overpowering scent. If a bar smells faint, melt and pour tells you at once, since there is no cure time to blame.

A base result far from the mould volume is a sign of a measuring slip, because the two should nearly match. If a 500 cm3 mould asks for 700 g of base, recheck the volume or the units.

🧮 Calculation formulas

The base follows from the mould volume and the density of melt and pour soap, which is close to 1 gram per cubic centimetre. Fragrance and colour are then percentages and rates on that base weight.

Base (g) = mould volume in cm3 x density, where density is about 1.0 for most bases.

Fragrance (g) = base weight x load percent / 100.

Colorant follows a rate per pound of base, so pounds of base = base grams / 453.6, and colorant in teaspoons = rate x pounds. Bars = base weight / bar weight, and per-bar fragrance = fragrance / bars.

Work the default: a 500 cm3 mould at density 1.0 is 500 g of base. Fragrance at 2 percent is 500 x 0.02 = 10 g. A medium colour at 0.25 tsp per pound is 0.25 x (500 / 453.6) = 0.28 tsp. At 100 g a bar, the mould makes 5 bars.

Melt and pour holds fragrance to about 3 percent, roughly half a cold process ceiling, because there are no free oils to bind extra scent. That is why a fragrance oil dosed for cold process weeps when it is used at the same rate in a melt and pour bar.

The base type shifts the density and the look a little. Clear glycerin bases are near 1.0, while whitened and enriched bases run a touch heavier and hold colour differently. The table below gives the practical differences.

🎨 Practical examples

Each example lists the mould, the base, the loads and the bars, then the amounts and what the soaper does with them.

1. Small clear loaf. 500 cm3 mould, clear base, 2 percent fragrance, medium colour, 5 bars. Base 500 g, fragrance 10 g, colour about 0.28 tsp mica. A clean single-colour bar.

2. Guest soap cavities. 250 cm3 total, white base, 2 percent, pastel colour, 5 small bars. Base 250 g, fragrance 5 g, colour about 0.06 tsp. Cavity moulds set the bar size for you.

3. Large white loaf. 1200 cm3 mould, white base, 2 percent, medium colour, 12 bars. Base 1200 g, fragrance 24 g, colour about 0.66 tsp. A full production loaf.

4. Two-layer bar. A 600 cm3 mould split into a 300 cm3 clear layer and a 300 cm3 white layer. Each layer takes 300 g of base and 6 g of fragrance at 2 percent, poured and set one at a time.

5. Maximum fragrance. 500 cm3 clear base at 3 percent. Base 500 g, fragrance 15 g. Melt and pour holds fragrance only to about 3 percent. Past this the bar sweats rather than smelling stronger.

6. Bold colour in clear base. 500 cm3 clear base, bold colour at 0.5 tsp per pound. About 0.55 tsp mica, which reads vividly in the transparent base and can bleed if a lighter layer sits beside it.

7. Filling from mould dimensions. A 20 by 8 by 6 cm loaf is 960 cm3, so it takes about 960 g of base and 19 g of fragrance at 2 percent. Dimensions convert to volume, then straight to base.

My first melt and pour loaf sweated little beads of oil for a week. I had used my cold process fragrance rate of 5 percent. Dropping to 2 percent gave a dry, clean bar that still smelled fine.

8. Over-fragrancing, edge case. 500 cm3 clear base at 5 percent gives 25 g of fragrance, well over the base’s capacity. The excess weeps out as an oily film, the bar feels greasy, and the scent is no stronger than at 3 percent.

9. Embeds in clear base. Small coloured shapes set first, then clear base poured around them. Calculate the clear base for the mould volume minus the embed volume, so the pour fills to the top without overflow.

💡 Tips and best practices

Melt the base gently in short bursts, stirring between each, and stop as soon as it is liquid. Overheated glycerin base turns rubbery and cloudy, and a scorched clear base never recovers its transparency.

Cut the base into small, even cubes before melting. Uniform pieces melt at the same rate, which avoids the scorched edges and unmelted lumps that come from melting one large block.

Keep a spray bottle of isopropyl alcohol at hand. A spritz on the surface pops the bubbles that form when you stir, and a spritz between layers helps them bond so the bar does not split later.

Add fragrance and colour near 60 degrees Celsius, not straight off the heat. Cooler base holds scent better and gives you a moment to stir colour in evenly before it starts to skin over.

Disperse mica in a little glycerin or rubbing alcohol before adding it, rather than dropping powder into the base. Melt and pour sets fast, and a clump you did not break up stays a clump in the bar.

Keep fragrance at or below 3 percent and colour light, especially in clear base. The transparency that makes clear base beautiful also shows every fault, so a lighter hand reads cleaner than a heavy one.

Work quickly once everything is in. Melt and pour starts setting as it cools, so have the mould ready, the colour dispersed and the fragrance measured before you remelt the last time.

Wrap finished bars promptly. Melt and pour is high in glycerin, which draws moisture from the air, so an unwrapped bar develops surface dew within a day.

⚠️ Common mistakes to avoid

Overheating the base

Melting too hot or too long makes clear base cloudy and any base rubbery, and the damage does not reverse.

Boiled melt and pour base turns tough and hazy for good. Overheating a clear base past its melt point ruins the transparency permanently. Melt in short bursts and stop at liquid.

Use short microwave intervals or a low double boiler, and stir between each rather than walking away.

Over-fragrancing

Using a cold process fragrance rate leaves more oil than the base can hold, and it sweats out.

Keep fragrance at 1 to 3 percent of the base weight. A bar that beads oil on the surface was fragranced past what melt and pour can carry.

Adding scent while too hot

Fragrance stirred into near-boiling base evaporates before the bar sets, wasting it and weakening the scent.

Pouring fragrance into base fresh off the heat lets half of it flash off. The pot smells wonderful and the bar smells of little. Cool to about 60 degrees first.

Let the base cool until it is still fluid but no longer steaming, then add scent and pour without delay.

Skipping the alcohol spritz

Bubbles on the surface and poor bonding between layers both trace back to missing the alcohol step.

Spritz the surface after pouring and between layers. It clears bubbles and helps a second layer grip the first.

Filling to the very top

A mould filled to the brim overflows the moment you spritz or nudge it, and melt and pour sets before you can mop it up neatly.

Leave a few millimetres of headroom. The near-1 density means the base weight already matches the volume closely, so a small margin is enough.

Leaving bars unwrapped

The glycerin that makes melt and pour clear also pulls water from the air, so bare bars go dewy and soft.

Wrap each bar in film or shrink wrap soon after unmoulding. It keeps the surface dry and the bar crisp.

🎯 When to use this calculator

Reach for it whenever you fill a new mould or plan a melt and pour batch. The base weight turns an unfamiliar mould into a known amount to buy and melt, with the fragrance and colour sized to match.

It matters for layered and embed designs, where you fill part of a mould at a time. Splitting the volume by layer keeps each pour the right size so the finished bar reaches the top without a gap or a spill.

Use it to plan a production run. Totalling the base across many moulds tells you how much to order, and the fragrance grams tell you how much scent the run will use.

I plan every craft-fair batch from the mould volumes now. Adding up the base weight tells me exactly how many kilos to order, so I stop guessing and running short of my clear base.

You can skip it for a mould and recipe you pour constantly and know by weight. This tool earns its place on new moulds, layered designs and buying for a run, not on a repeat you already have measured.

🔗 Related calculators

• Soap mould volume calculator
• Soap fragrance usage calculator
• Soap colorant quantity calculator
• Soap lye calculator
• Liquid soap dilution calculator
• Soap additives calculator
• Soap batch resize calculator
• Soap cost per bar calculator

📖 Glossary

Melt and pour – a ready-made soap base that is melted, scented, coloured and moulded, without lye or cure.

Glycerin base – a clear melt and pour base high in glycerin, prized for transparency.

Base weight – the weight of melt and pour base, the figure fragrance and colour are dosed against.

Embed – a small pre-made shape set into a bar, often coloured soap inside a clear base.

Layering – pouring one colour, letting it set, then pouring the next for a striped bar.

Why does melt and pour need no cure? Because the soap is already made. Melting only changes its shape, so a bar is usable as soon as it hardens, unlike cold process which cures for weeks.

Sweating – beads of moisture or oil on a bar, from glycerin drawing water or from over-fragrancing.

Alcohol spritz – a spray of isopropyl alcohol to clear surface bubbles and bond layers.

Flash off – fragrance evaporating when added to base that is too hot.

Headroom – the small gap left at the top of a mould to prevent overflow.

Density – the weight per volume of the base, near 1 gram per cubic centimetre for most melt and pour.

❓ Frequently asked questions

How much base do I need for my mould?

About the same number of grams as the mould’s volume in cubic centimetres, because melt and pour is close to the density of water. A 500 cm3 mould takes roughly 500 g of base.

Measure an odd mould by filling it with water and weighing it. That weight in grams is your base weight, whatever the shape.

Why does my bar sweat?

Two reasons. Glycerin in the base pulls moisture from the air, and over-fragrancing leaves oil that beads on the surface.

Wrap bars promptly to stop the moisture, and keep fragrance at or below 3 percent to stop the oil. Both together keep the surface dry.

How much fragrance can melt and pour hold?

About 1 to 3 percent of the base weight, roughly half what cold process takes. The base has no free oils to bind extra scent.

On a 500 g base, 2 percent is 10 g and 3 percent is 15 g. Above 3 percent the bar sweats instead of smelling stronger.

Can I use any colorant?

Use cosmetic-grade micas, liquid soap dyes or oxides made for soap, and check each is skin-safe. Clear base shows colour vividly, so start light.

Food colouring fades in soap and is not a substitute. Craft colours may not be skin-safe, so buy from a soap supplier.

What temperature should I add fragrance?

Around 60 degrees Celsius, once the base has cooled from melting but is still fluid. Hotter than that and the scent flashes off.

Cooler base holds scent and colour better, so patience between melting and pouring pays off in the finished bar.

Stir the fragrance in gently to avoid bubbles, then pour before the base skins over.

Do I need to cure melt and pour soap?

No. The soap is already saponified, so a bar is ready to use as soon as it sets, usually within an hour or two.

This is the main advantage over cold process, which needs four to six weeks of cure before it is mild enough to use.

How do I calculate a layered bar?

Split the mould volume by layer and treat each as its own small pour. A 600 cm3 mould in two equal layers is two 300 cm3 pours of 300 g each.

Spritz alcohol between layers so they bond, and let each set before pouring the next to keep the line crisp.

Can I remelt leftover base?

Yes, melt and pour can be remelted several times, which makes it easy to reuse trimmings and failed pours.

Each remelt loses a little water and clarity, so remelt gently and avoid overheating to keep a clear base transparent.

⚖️ Disclaimer

This calculator provides educational estimates for sizing a melt and pour batch. It is a planning aid for hobby and small-batch soapers, not a precise measurement of a finished bar.

Base density and fragrance capacity vary by brand and base type, so the base, fragrance and colour figures are approximations. Measure a new mould with water and follow the instructions on your specific base.

Use cosmetic-grade, skin-safe fragrance and colorants, and follow the supplier’s usage limits. Patch test a new fragrance or colorant before selling or gifting.

Melt and pour base is hot when melted and can burn. Melt gently, avoid overheating, and take care pouring, since the base sets quickly once it starts to cool.