How to scale a craft recipe
The arithmetic is the same in all five crafts. What differs is the single line in each one that has to go back through its own calculator.
Divide the batch you want by the batch the formula makes, then multiply every line by that factor — 635 g as written becomes 1.27 kg at double. The ratios inside the formula never change, which is what makes the result the same recipe rather than a new one. The exceptions are per craft: a soap recipe’s lye is recalculated from its oils rather than scaled, and a resin pour’s depth ceiling does not move with batch size at all.
Almost every craft formula you will ever be handed was written for someone else’s mould, someone else’s jar or someone else’s market stall. Scaling it is the most ordinary thing a maker does, and it is genuinely simple: one division to find the factor, one multiplication per line. Nothing else about the recipe changes.
The reason it has a reputation for being risky is that each of the five crafts on this site has exactly one line that does not obey that multiplication — and in soap’s case, getting it wrong produces a bar that burns skin. Knowing which line, in which craft, is the whole of the difficulty. Everything else is a calculator.
This page covers the arithmetic first, then the exception in each craft, then the practical limits — because a formula that scales perfectly on paper can still be a batch that will not fit in your pot. The batch size calculator does the multiplication for any craft and names the exception for the one you pick.
One formula at four batch sizes
Every line moves by the same factor, so every ratio inside the formula is untouched. The fragrance column is the one to watch — it is the first line to become unweighable when you scale down.
Three ways to say how big you want it
The direct version, and the right one when you simply want more of something that already works. A factor below 1 shrinks a batch by exactly the same arithmetic.
The one to use when you know what you have to deliver rather than what you want to mix. Divide the items you need by the items the formula makes.
Best when you are filling a mould or a vessel of known capacity. The same formula, currently 635 g, taken to a stated finished weight.
The line that does not scale, craft by craft
The lye. It is worked out from which oils are in the blend, not from how much batter there is — scaling it alongside the oils happens to agree while the blend is untouched and stops agreeing the moment an oil is swapped. Recalculate it from the resized oils through the lye calculator every time, and the answer is right in both cases. See how a soap calculator actually works for what it is doing with those numbers.
The pour depth, which is not a scaling question and is the one that matters. A bigger batch poured into the same mould is a deeper pour, and every system has a depth ceiling above which it overheats. Pouring a doubled batch into the same mould is not a bigger batch, it is a deeper one, and the ceiling is a heat hazard rather than a slow cure. The epoxy calculator works out how many lifts the new depth needs.
A formula written in drops. Drop size varies with the material and the pipette, so scaling drops multiplies that error rather than cancelling it — convert to grams once, then scale the grams. Convert the formula to grams once, with each material’s own density, and the scaled version is repeatable. The formula scaler does the conversion and the scale in one pass.
Wick size, which does not scale at all. It follows the container diameter, and pouring twice as much wax into the same jars changes nothing about it. It is decided by the container diameter and the wax, so it is unchanged by how much you pour — see the wick size chart. What does change is how many jars you need, which is worth counting before you melt anything.
The wetting liquid, which is a feel job rather than a measurement. Humidity moves it more than batch size does, so spritz to the same damp-sand texture rather than multiplying the millilitres. Everything else in a bath bomb scales cleanly, including the fizz ratio, which is why the bath bomb recipe scaler resizes the dry ingredients and leaves the spray bottle to you.
Where scaling goes wrong in practice
A recipe written as weights fits exactly one mould. The same recipe written as shares of a base fits every mould you will ever own. It takes one pass to convert and it is the reason published soap and perfume formulas are written that way.
Scaling down is where formulas break, and it always breaks at the small line first. The 15.0 g of fragrance above is fine at any scale-up; at 0.07× it is down to a single gram, and a scale that reads in whole grams is now rounding away a meaningful share of it.
A five-times batch is five times the volume in a pot that has not changed size, five times the pour time against a pot life that has not changed either, and five times the mould space. The maths will happily hand you a batch you cannot physically make.
Cure times, cook stages, maceration and cure loss are properties of the chemistry rather than of the quantity. A double batch of cold process soap still cures for the same weeks; a double batch of perfume still needs its month.
Resize your own formula
Enter it as printed or as percentages, pick a target — a multiplier, an item count or a finished weight — and every line comes back resized, with your craft’s exception named.
Open the batch size calculator →Estimates, not advice. Every figure on this page is computed from published reference values and standard measures, so your own inputs, equipment and conditions will move it. Nothing here is professional advice — talk to a qualified professional before acting on it.