Cost Per umol Calculator

A mole is a fixed count of particles, so two micromoles of anything contain the same number of molecules. A milligram has no such property, because the mass of a fixed number of molecules is set by the molar mass of the substance, and that differs between peptides by the number of residues and by any modifications present. A given mass of a short peptide therefore contains far more molecules than the same mass of a long one, and dividing price by mass rewards the heavier peptide for a reason that has nothing to do with what a molecule costs.

That is the whole reason this page sits beside the cost per milligram calculator . Cost per milligram answers what this material costs, which is the right question when one material is being bought in different pack sizes. Cost per micromole answers what a particle count costs, which is the right question when the materials being compared are different substances. Neither is more correct than the other, and using one where the other belongs produces a confident answer to a question nobody asked. Choosing between them is a decision about what the two numbers are meant to represent, and it is worth making explicitly before either figure is quoted.

The only input this page adds is a molar mass, and it carries more weight than any other. The calculation is a mass converted into a particle count, and the conversion factor is the molar mass, so an error there scales the answer directly and in proportion. There is no check against the result, because the calculator has no second opinion on how heavy a molecule is. Deriving the figure from a sequence gives a defensible number; guessing it from the size of the peptide does not. The average molecular weight calculator computes one from a sequence, and the mass to moles calculator performs the same division on its own.

It is worth keeping the distinction between an average molecular weight and a monoisotopic mass in mind when sourcing a molar mass, because the two are close but not identical and the gap widens as a peptide gets longer. Neither is wrong for this purpose, but mixing a monoisotopic figure into a quantity that came from a weighed mass introduces a small systematic offset that has no sign you could guess. The molar mass cross check calculator compares figures from different sources, and the molarity calculator uses the same molar mass in the opposite direction, from a mass and a volume to a particle concentration.

This page returns both a cost per micromole and the total number of micromoles in the quantity, and the second number is the one to read first. It is the denominator, so it tells you immediately whether the price was divided by a particle count in the hundreds or in the millions, which are very different situations and look identical once a currency is attached. A container holding a few hundred micromoles and one holding a few thousand are being priced per particle count at very different densities, and the cost per micromole is what exposes that.

The ratio between the two results is also a check on the molar mass. Given a cost per milligram and a cost per micromole for the same material, the molar mass in grams per mole follows directly from one figure divided into the other. If that recovered value does not match the molar mass entered, one of the three numbers is wrong, and this is a cheap way to find out before the comparison is used. The molar concentration converter covers the case where a concentration is quoted in molar terms and a mass basis is needed instead.

Like the milligram version, this is a comparison figure and not a total. It prices a particle count and nothing else, so shipping, consumables and unused material are all excluded, and on a small quantity they can exceed the vial price. It also does not adjust for purity: a cost per micromole of impure material reads lower than the same material purity corrected, because the mass divided by included matter that is not peptide. That correction is a division by the purity fraction applied to the mass, and it is cleanest done before the molar mass is used, because that keeps each step a single division with one job.

The final caveat is that a lower figure describes price only. Nothing in this arithmetic speaks to quality, consistency between batches, or suitability for any purpose, and a material can be cheap per micromole and still be the wrong choice. Where a comparison needs more than a price, the honest conclusion is that the arithmetic has done its part and the remaining questions need documentation rather than another calculator. For the general reason a mass basis and a molar basis cannot be compared without a molar mass, the molarity versus mass concentration guide sets out where the two scales can and cannot be interchanged.