Free calculator
Batch scaling calculator
A formula scales by one number applied to every line. The mistake is rounding line by line as you go, which is how a blend that worked at 50 grams comes out wrong at 500.
The sum, in words
Divide the batch you want by the batch you have. That gives one factor, and every line in the formula is multiplied by it. Going from 50 g to 500 g is a factor of 10, so a line of 0.85 g becomes 8.5 g and a line of 12 g becomes 120 g.
It works downward in exactly the same way. Going from 500 g to 40 g is a factor of 0.08, and every line shrinks by it.
The mistake that ruins a scaled batch
Rounding each line as you go. It feels tidy: 8.47 g becomes 8.5, 0.62 g becomes 0.6, and each one is only a little out. But the roundings do not cancel. Some go up, some go down, and on a formula of forty lines the proportions at the end are not the proportions you started with, in a way that is invisible on the sheet and audible in the bottle.
Carry the full figure through, round only at the point of weighing, and let the total land where it lands rather than forcing it back to a round number.
Scaling down hits a floor
Scaling up is arithmetic. Scaling down runs into the balance. A line that was 0.4 g in a 500 g batch is 0.032 g in a 40 g one, and at that point you are below the minimum weight of most bench balances and the number on the display is inside the instrument's own error rather than being a measurement.
The answer is not a smaller number, it is a dilution. Weigh a larger, honest amount of a weaker solution instead. That is what dilutions are for, and it is why a formula built on them scales down further than one built on neat materials.
What does not scale with the factor
The compliance answers do not change, and that is worth being clear about because people assume a bigger batch is a bigger problem. Every limit and every threshold is a percentage, and percentages are unaffected by how much you make. A formula that was compliant at 50 g is compliant at 50 kg, at the same category and the same strength.
What does change is everything physical. Maceration takes longer in a larger volume, filtration is a different job, and the loss left in the vessel is a smaller share of a big batch than of a small one. And a new batch is a new batch record with a new number, regardless of it being the same formula as last time.
What this calculator does not do
It gives you the factor and shows what one line becomes. It does not hold your formula, so it cannot apply the factor to forty lines, check the total, or tell you which scaled-down line has fallen under your balance's minimum weight. That is the arithmetic worth having done for you rather than done once by hand.