Peptide calculator.
Enter the vial strength and the volume of bacteriostatic water added. The calculator returns the solution concentration and the volume containing your target mass, read off as syringe graduations.
Syringe volume
Peptide in the vial
Bacteriostatic water added
Mass to draw
5units
= 0.05 mL on a 1 mL syringe
- Concentration
- 5 mg/mL
- Per unit
- 50 mcg
- Draws per vial
- 40
- Target mass
- 0.25 mg
Saved calculations stay in this browser. Nothing is uploaded.
A peptide calculator is a dilution calculator with a specific vial in front of it. You give it two numbers, the mass of solid in the vial and the volume of diluent you are adding, and it returns the concentration of the solution that results. Give it a third number, the mass you want in solution, and it returns the volume of that solution containing it. That is the whole of the operation: no chemistry beyond division, and nothing about the compound itself.
The arithmetic is not difficult. It goes wrong anyway, and almost always in the same four places: confusing micrograms with milligrams, reading syringe units as millilitres, assuming every barrel is graduated the same way, and calculating from the strength printed on the label rather than the mass a laboratory actually measured. The last of those is the one nobody mentions, and it is the largest.
What follows explains each division, what moves the answer and what leaves it alone, a reference table of concentrations across common diluent volumes, and the ways the result ends up wrong. It is arithmetic for preparing a solution of known concentration in a laboratory. It is not guidance about administering anything to anyone.
What a peptide calculator actually computes
Two divisions and one unit conversion. The first division is mass over volume. A vial holding 10 mg of solid, reconstituted in 2 mL of diluent, gives a solution at 10 divided by 2, which is 5 mg/mL. Every millilitre of that liquid carries 5 mg of solid, and every 0.1 mL carries 0.5 mg. Nothing else in the calculation matters until this figure is right.
The second division goes the other way. Take the mass you want in solution and divide it by the concentration you have just worked out, and the result is a volume in millilitres. At 5 mg/mL, a target mass of 0.5 mg is 0.5 divided by 5, which is 0.1 mL. The unit conversion at the end turns that volume into the graduations printed on an insulin syringe barrel by multiplying by 100, so 0.1 mL reads as 10 units.
Much of the traffic to pages like this one arrives by searching for a peptide dosage calculator, so it is worth being precise about what that phrase does not describe here. This tool computes concentration and volume. It has no knowledge of the compound in the vial and no opinion about quantity. It is the same arithmetic you would run on a salt solution, which is why a peptide calculator and a general dilution calculator return identical numbers from identical inputs.
None of it is specific to peptides. What is specific to peptides is the input: a vial of lyophilized powder whose true mass of peptide is not the number printed on the glass. That is the next section, and it is the one part of this page that changes anybody's answer.
Why the number on the vial is not the mass of peptide in it
A label strength is a target for the fill, not a measurement of the contents. The measurement is on the certificate of analysis, reported as net peptide content: the mass of peptide the testing laboratory found, set against the strength on the label. It is a different figure from HPLC purity, which is an area percentage describing the share of what the detector registered rather than a mass of anything.
Across the 42 lots published in the COA library that report a net peptide content, the measured figure runs from 93.6% of label to 131.6% of label, with a median of 107.9%. The spread is not evidence of anything sinister: fills are set above target so the labelled mass survives residual water and a counter-ion such as trifluoroacetate, and some land further above than others. It does mean a calculation built on the label alone can be several per cent out, in either direction, before you have made a single mistake.
Put numbers on it. A vial labelled 10 mg reconstituted in 2 mL gives a nominal 5 mg/mL. If the certificate for that lot reports 93.6% of label, the vial holds 9.36 mg, and 9.36 divided by 2 is 4.68 mg/mL. At the other end, 131.6% is 13.16 mg, and 13.16 divided by 2 is 6.58 mg/mL. At the median of 107.9% the vial holds 10.79 mg and the solution is 5.40 mg/mL, about 7.9% stronger than the label figure. Same vial, same 2 mL, three different answers, and only one of them came from a measurement.
So the useful input to the first division is the measured content for your lot, not the number on the glass. Where a certificate omits it, the honest position is that the mass is unknown and the concentration is an estimate: one of the things how to read a peptide certificate of analysis sets out line by line, and a question worth asking under how to vet a research peptide supplier.
Two neighbouring figures get confused with content often enough to separate here. Peptide purity is chromatographic area percent and says nothing about mass. Peptide purity testing describes how both numbers are produced and by whom. Content is the only one of the three that belongs in a division.
Insulin syringe units: the conversion at the end of a peptide calculator
The U-100 convention comes from insulin, which is standardised at 100 units per millilitre. A barrel built for it is therefore graduated so that 100 marks span 1 mL, which makes one mark one hundredth of a millilitre, 0.01 mL. That is the entire definition. The graduation is a volume, printed on glass or plastic, and it was printed before anybody knew what would be in the barrel.
Which is why 0.05 mL is 5 units whatever is dissolved in it: water, saline, a 2 mg/mL solution or a 20 mg/mL one. A unit is not a mass, it does not become a mass when a peptide is present, and two solutions at different concentrations reading the same number of units contain different masses of solid. Any sentence of the form "the answer is 10 units" is incomplete without the concentration it was calculated from.
The conversion runs both ways: volume in millilitres multiplied by 100 gives units, units divided by 100 gives millilitres. The table sets the correspondence out, with the mass alongside it at one nominal concentration so the two columns can be told apart at a glance.
| Volume | U-100 units | Mass at 5 mg/mL |
|---|---|---|
| 0.05 mL | 5 units | 0.25 mg |
| 0.10 mL | 10 units | 0.5 mg |
| 0.20 mL | 20 units | 1 mg |
| 0.25 mL | 25 units | 1.25 mg |
| 0.50 mL | 50 units | 2.5 mg |
| 1.00 mL | 100 units | 5 mg |
What changes the answer and what does not
Diluent volume is the only input on this page that moves the concentration once the mass is fixed. It moves it inversely: halve the volume and the concentration doubles, double the volume and it halves. A 10 mg vial gives 10 mg/mL in 1 mL, 5 mg/mL in 2 mL and 2 mg/mL in 5 mL. The mass of solid never changed. Only the amount of liquid it is spread through did.
The identity of the diluent does not enter the arithmetic at all. Two millilitres of bacteriostatic water and two millilitres of plain sterile water produce the same concentration from the same vial, because concentration is mass over volume and neither liquid contributes mass to the solute. What differs between them is the preservative and therefore the handling, which is the subject of sterile water vs bacteriostatic water and, for the composition itself, what is bacteriostatic water.
Displaced volume is small but real, and worth arithmetic rather than a footnote. Ten milligrams of solid is 0.01 g, and at a density near 1 g/mL it occupies roughly 0.01 mL. Adding 2 mL of diluent therefore gives about 2.01 mL of solution, so the true concentration is nearer 4.98 mg/mL than 5.00 mg/mL: an error of about half a per cent. That is an order of magnitude smaller than the fill variation above, which is the honest reason most calculators ignore it.
Time and temperature change nothing in the division either, though they do change what remains in solution to be measured, which is a different problem and a real one. How to store peptides covers the solid and the solution; bacteriostatic water storage covers the two clocks on a diluent vial.
Peptide reconstitution chart, with the working shown
A peptide reconstitution chart is the first division tabulated in advance. Find the label strength down the side, the diluent volume across the top, and read off the concentration. Every cell is the strength divided by the volume, rounded to two decimal places where it does not divide cleanly. Nothing here is a recommendation about what to prepare; it is long division, published so it can be checked.
| Vial strength (label) | 1 mL diluent | 2 mL diluent | 3 mL diluent | 5 mL diluent |
|---|---|---|---|---|
| 2 mg | 2 mg/mL | 1 mg/mL | 0.67 mg/mL | 0.4 mg/mL |
| 5 mg | 5 mg/mL | 2.5 mg/mL | 1.67 mg/mL | 1 mg/mL |
| 10 mg | 10 mg/mL | 5 mg/mL | 3.33 mg/mL | 2 mg/mL |
| 15 mg | 15 mg/mL | 7.5 mg/mL | 5 mg/mL | 3 mg/mL |
| 20 mg | 20 mg/mL | 10 mg/mL | 6.67 mg/mL | 4 mg/mL |
| 30 mg | 30 mg/mL | 15 mg/mL | 10 mg/mL | 6 mg/mL |
Two worked examples, end to end
First, a stock solution from a 10 mg vial and 2 mL of diluent. The concentration is 10 divided by 2, which is 5 mg/mL. A target mass of 0.5 mg is 0.5 divided by 5, which is 0.1 mL, and 0.1 multiplied by 100 is 10 units on a U-100 barrel. Now apply the lot figure: if the certificate reports 107.9% of label, the vial held 10.79 mg, the stock is 5.40 mg/mL, and the volume holding 0.5 mg is 0.5 divided by 5.40, which is 0.093 mL, or between 9 and 9.5 units. The label calculation was out by roughly 7%, all of it invisible.
Second, a 5 mg vial and 2.5 mL of diluent. The concentration is 5 divided by 2.5, which is 2 mg/mL. A target mass of 250 mcg is 0.25 mg, and 0.25 divided by 2 is 0.125 mL, which is 12.5 units. That figure sits between two graduations on a barrel marked in whole units, so the reading is an estimate. Had the same vial gone into 2 mL, the stock would be 2.5 mg/mL and the same 0.25 mg would be 0.1 mL, landing on the 10 unit mark exactly. Which to prepare is not a question this page answers; the point is that the choice of volume decides whether the answer lands on a graduation or between two of them.
Reversing either example is the cheapest check available. Multiply the volume by the concentration and the target mass should come back: 0.1 mL at 5 mg/mL is 0.5 mg, 0.125 mL at 2 mg/mL is 0.25 mg. If it does not, the error is in the arithmetic rather than anywhere more interesting.
Where a peptide calculator gives the wrong answer
Micrograms entered as milligrams. There are 1,000 mcg in 1 mg, so 250 mcg is 0.25 mg and 1,500 mcg is 1.5 mg. Typing 250 into a field expecting milligrams asks for a thousand times the mass intended, and the answer that comes back usually exceeds the liquid in the vial, which is the tell.
Units read as millilitres. Ten units is 0.1 mL, not 10 mL: a factor of 100, and 10 mL will not fit in a 1 mL barrel anyway. Any answer above 100 units has either overrun the barrel or started from the wrong concentration.
Label strength used in place of measured content. This is the quiet one, because the arithmetic is correct and the input is not. Look the lot up in the COA library or through the lot verification page, read the net peptide content, and put that mass into the first division instead. Where a vial in the research peptide catalogue carries a certificate with the figure on it, that figure is the mass to calculate from.
Assuming every barrel is U-100. U-40 and U-50 syringes exist, and on a U-40 barrel one unit is 0.025 mL rather than 0.01 mL, so the same volume reads as a different number of units. The conversion is printed on the barrel. Read it before trusting any figure a calculator returns in units.
Two smaller ones close the list. Adding more diluent later does not leave the earlier concentration valid: the mass is unchanged, the volume is not, so the figure has to be recalculated from the new total. And the volume of diluent added is not quite the final volume of the solution, for the displacement reason above, though at these masses that is a fraction of a per cent.
Every one of these is a checkable error, which is the argument for publishing the working rather than only the result. A peptide calculator is two divisions and a conversion, and each of them can be reversed by hand in a few seconds. The input that cannot be checked by hand is the mass in the vial, which is why the certificate matters more than the calculator does, and why the rest of the research library spends more time on measurement than on arithmetic.
Common questions
What does a peptide calculator do?
It performs dilution arithmetic. Divide the mass of solid in the vial by the volume of diluent added and you get the concentration of the resulting solution in mg/mL. Divide a target mass by that concentration and you get the volume of solution containing it, in millilitres, which multiplied by 100 is the reading in U-100 syringe graduations. It computes concentration and volume, nothing else.
Is a peptide reconstitution calculator the same thing?
Yes. A peptide reconstitution calculator and a peptide calculator describe the same two divisions: mass over volume for the concentration, target mass over concentration for the volume. The word reconstitution refers to the laboratory operation of dissolving a lyophilised solid in a diluent to reach a known concentration, which is what the first division describes.
What about a peptide dosage calculator?
That is a common search phrase rather than a description of this tool. What the arithmetic here returns is a concentration in mg/mL and a volume in millilitres or syringe graduations. It has no knowledge of the compound in the vial, no biological model behind it, and nothing to say about quantity, suitability or administration. These are research chemicals and this page is dilution arithmetic for laboratory use.
How do you reconstitute peptides, in arithmetic terms?
As arithmetic it is three steps. Establish the mass of peptide in the vial, using the net peptide content on the certificate rather than the strength on the label. Decide the volume of diluent, which is the only input that moves the concentration. Divide the first by the second for mg/mL. Anything beyond that is handling rather than arithmetic: bacteriostatic water for peptides covers the diluent side and what is lyophilized powder covers the solid.
Is a bac water calculator different from this one?
No. A bac water calculator is this arithmetic with bacteriostatic water named as the diluent. The identity of the liquid does not appear in the division: 2 mL is 2 mL whether it is bacteriostatic water or sterile water, and the concentration that results is identical. The difference between the two liquids is the preservative and the handling that follows from it, not the mathematics.
What is a peptide dilution calculator for?
Diluting a solution you already have, rather than a solid. The relation is C1 multiplied by V1 equals C2 multiplied by V2. To take a stock at 5 mg/mL down to 1 mg/mL in a final 1 mL: 1 multiplied by 1 divided by 5 is 0.2 mL of stock, made up with 0.8 mL of diluent. Volumes add, mass does not change, and the concentration falls in proportion.
How many units is 0.5 mL on an insulin syringe?
Fifty, on a U-100 barrel. The U-100 convention graduates 1 mL into 100 marks, so one unit is 0.01 mL and 0.5 mL is 50 of them. On a U-40 barrel the same 0.5 mL reads as 20 units, because a unit there is 0.025 mL. The conversion is printed on the barrel and should be read rather than assumed.
Does one insulin syringe unit mean one milligram?
No. A unit is a volume graduation, one hundredth of a millilitre on a U-100 barrel, and it was printed on the plastic before anything was dissolved in it. The mass sitting in one unit depends entirely on the concentration of the solution: 0.01 mL holds 0.05 mg at 5 mg/mL and 0.2 mg at 20 mg/mL. A figure in units means nothing without the concentration it came from.
Does adding more bacteriostatic water reduce the amount of peptide?
No. The mass of solid in the vial is fixed at the moment it was filled. Adding more diluent spreads that same mass through more liquid, so the concentration falls and the volume containing any given target mass rises in proportion. A 10 mg vial holds 10 mg whether it goes into 1 mL or 5 mL; the first is 10 mg/mL and the second is 2 mg/mL.
Why does my calculation not match the certificate?
Usually because the calculation started from the label strength. The label is a fill target; the certificate's net peptide content is the measured mass. Across the 42 lots in the COA library reporting that figure it runs from 93.6% to 131.6% of label, with a median of 107.9%, so a label-based concentration can be several per cent adrift in either direction before any arithmetic error is involved.
What is net peptide content and why should the calculation use it?
It is the mass of peptide a laboratory measured in the vial, reported against the label strength. It is the only figure on a certificate that is a mass, which is why it belongs in a division where every other input is a mass or a volume. HPLC purity is an area percentage describing the share of what the detector registered and cannot be substituted for it, a distinction how to read a peptide certificate of analysis sets out in full.
Is 250 mcg the same as 0.25 mg?
Yes. There are 1,000 micrograms in a milligram, so 250 mcg is 0.25 mg, 500 mcg is 0.5 mg and 1,500 mcg is 1.5 mg. Mixing the two units is the most common error in this arithmetic and it is out by a factor of 1,000, so the result is usually absurd: a volume larger than the vial, or a reading past the end of the barrel.
Does the powder itself change the final volume?
Slightly. Ten milligrams of solid is 0.01 g and occupies roughly 0.01 mL at a density near 1 g/mL, so 2 mL of diluent added to it yields about 2.01 mL of solution and a concentration near 4.98 mg/mL rather than 5.00 mg/mL. That is about half a per cent, considerably smaller than the lot-to-lot variation in the fill, which is why most calculators leave it out.
Where do I find the measured content for my lot?
On the certificate for that lot number. Every certificate held for this catalogue is published in the COA library, including lots no longer in stock, and a lot number can be checked directly through the lot verification page. Products carrying a certificate are listed in the research peptide catalogue, and how the testing is produced is covered in peptide purity testing.
Can sterile water be used instead, and does the arithmetic change?
The arithmetic does not change: concentration is mass over volume, and neither liquid contributes to the mass of the solute. What changes is that sterile water carries no preservative, so a container is single-use once its seal is broken, whereas a preserved vial can be entered repeatedly. The comparison is set out in sterile water vs bacteriostatic water, and the shelf-life clocks in bacteriostatic water storage.
No black box
Two divisions and a unit conversion. Published so you can check it against your own working rather than trusting ours.
vial mass (mg) ÷ diluent volume (mL) = mg/mL
10 mg reconstituted in 2 mL gives 5 mg/mL.
target mass (mg) ÷ concentration (mg/mL) = mL
250 mcg is 0.25 mg; at 5 mg/mL that is 0.05 mL.
volume (mL) × 100 = units
An insulin syringe is marked in U-100 units, where 100 units = 1 mL. That convention comes from insulin and has nothing to do with peptide mass, 0.05 mL is 5 units regardless of what is dissolved in it.
For laboratory research use only. This tool performs dilution arithmetic for preparing solutions of known concentration in a laboratory setting. It is not dosing guidance, it does not account for any biological variable, and nothing here implies these compounds are suitable for administration to humans or animals. All compounds listed on this site are sold strictly as reference materials for in-vitro laboratory research conducted by qualified professionals. They are not drugs, foods, cosmetics, or medical devices. They are not intended for human or veterinary consumption, therapeutic use, diagnostic application, or any in-vivo use whatsoever. These statements have not been evaluated by the Food and Drug Administration. By purchasing, you affirm that you are a qualified researcher and that you will comply with all applicable institutional, local, state and federal regulations governing the handling of research chemicals.