Cost Per Sample Calculator

The single input that decides whether this figure means anything is the sample count, and it has to be the number actually obtained rather than the number expected. A batch that yields fewer samples than it was planned to yield has still cost what the planned batch cost, so dividing by the planned count understates the real figure, and the shortfall is usually larger than the arithmetic suggests because a failed attempt consumes most of the materials. The yield percent calculator makes the difference between a theoretical and an actual yield explicit before it ever reaches this division.

A related distinction is between samples and measurements. Material consumed as a quality control check, retained as a reference, or held back as a spare still cost what they cost, so including them in the denominator gives a lower per sample figure than excluding them does. Both conventions exist and neither is wrong, but mixing them between two projects makes the two figures incomparable, which defeats the purpose of computing either. Where a batch produces a mix, the honest description is an average, and the recovery percent calculator is useful for recording what a process actually yielded first.

Dividing a total by a count produces a mean, and a mean says nothing about the spread. If a batch is split evenly the mean is a fair description of any single sample. If it produces nine of one size and one of another, the mean describes a sample that does not exist, understating the common case and overstating the rare one. That is not a flaw in the calculation. It is a property of averages, and it is why the figure reads best next to the batch total it was taken from, which the batch cost calculator produces.

The way to make a mean describe a real sample is to change the denominator to match the question. Dividing by the number of samples of one particular size gives the cost of a sample of that size. Dividing by total amount delivered, expressed in the same mass units as the material, gives a cost per milligram delivered, which is a different and often more useful figure. Both are one division, and choosing between them is a matter of what the number is going to be compared against rather than of which is more accurate.

Cost per sample behaves as though every cost in the batch were fixed and every additional sample cost nothing to make. A real batch total mixes two kinds of cost: costs that recur whatever the batch size, and costs that recur with each sample, and this division cannot tell them apart. The batch scaling calculator performs the purely proportional scaling that assumes every cost behaves this way, which makes it the right place to see that assumption written down rather than hidden. A project carrying a large one-off component and one carrying a large repeatable component can therefore return the same figure at completely different underlying costs per sample.

The consequence is that two projects using the same material can show very different cost per sample figures with no difference in efficiency between them. One may have carried a large one-off cost that the second did not, or produced many more samples from the same fixed inputs. Because the arithmetic here cannot separate the two kinds of cost, a figure that looks poor may be entirely explained by the denominator. Establishing the batch total properly, with consumables and failed attempts included, is what makes the comparison worth making at all. Splitting a total into its fixed and repeatable parts before dividing is the only way to see which of the two is driving the number, and no field on this page performs that split for you.

The division is trivial, so all of the uncertainty sits in the numerator. A batch cost that omits failed attempts, purification, analyst time, or the consumables nobody invoiced will produce a per sample figure that is precise and wrong, which is the worst combination available. Building the list line by line instead of estimating it in one figure is the entire value of the step before this one, and the sample prep calculator is a reasonable place to itemise what a single preparation consumes in advance of writing the sheet up.

Currency is the other thing that has to be settled before two figures are compared. No conversion is applied here, so the result is in whatever units the batch cost was entered in, and two projects quoted in different currencies have to be converted before either is divided. Once both the numerator and the count are honest, the result is the amortised cost of producing one unit at one particular scale and nothing more than that. It is a project figure, it describes this batch, and it will not transfer to a different batch without recalculation.