The four conversions this tool handles
Mass conversions are pure decimal arithmetic: grams, milligrams, micrograms and nanograms each differ from the next by a thousand. Volume conversions are the same, with one wrinkle, which is that syringe units are a volume in disguise.
Concentration conversions relate mass to volume, and adding a molecular weight turns a mass concentration into a molar one. International units are the odd category out, because an IU is not a mass at all: it is a potency defined against a reference preparation, and the conversion factor is different for every substance.
Syringe units are hundredths of a millilitre
A U-100 insulin syringe carries one hundred marks per millilitre, so one unit mark is 0.01 mL. The converter treats units as a volume unit for exactly this reason, and the equivalence holds for any liquid in a U-100 barrel.
What does not carry over is the potency meaning. Insulin is standardised at 100 international units of activity per millilitre, which is why the barrel is marked that way. For anything else in a U-100 barrel, a unit is a volume and nothing more.
cc and mL are the same thing
A cubic centimetre and a millilitre are identical volumes. Syringes marked in cc and syringes marked in mL are marked in the same units under two names, and the converter treats them as equal because they are.
Why international units resist a general formula
An international unit is a unit of biological activity, fixed by a World Health Organization reference preparation rather than derived from a molecular weight. There is no arithmetic that turns IU into milligrams in general; each substance has its own factor, established by assay against its own standard.
The two factors this tool carries are the ones most often needed. Somatropin runs at three IU per milligram under the current standard, so one IU is about 0.333 mg. Human chorionic gonadotropin runs at roughly 10,800 IU per milligram, so one IU is about 0.0000926 mg, and a 5,000 IU vial holds about 0.46 mg of protein.
- •The factor is substance-specific. Applying a somatropin factor to anything else is meaningless.
- •Reference standards are revised. A factor from an older edition can differ from the current one.
- •A product's own labelling always beats a general conversion factor.
Percentage strength, in the form it actually appears
A concentration written as a percentage is almost always weight in volume: one percent means one gram in one hundred millilitres, which is ten milligrams per millilitre. That single relationship covers benzyl alcohol at 0.9 percent, saline at 0.9 percent and every other w/v figure on a vial label.
So bacteriostatic water at 0.9 percent benzyl alcohol is 9 mg/mL of benzyl alcohol, and 0.9 percent sodium chloride is 9 mg/mL of salt. The converter applies the same factor of ten in both directions.
Where molarity enters
Converting a mass concentration to a molar one needs the molecular weight, because molarity counts molecules rather than mass. A milligram of a 500 Da peptide is twice as many molecules as a milligram of a 1,000 Da one, and assay work that depends on receptor occupancy or stoichiometry cares about the count, not the mass.
Enter a molecular weight and the converter reports millimolar alongside the mass figures. The molarity calculator handles the same conversion with presets and a dilution mode attached.
How the unit converter works
Every category converts through one canonical unit, so a conversion and its inverse always agree. Mass goes through milligrams, volume through millilitres, concentration through milligrams per millilitre.
mass: value -> mg -> target unit volume: value -> mL -> target unit (1 unit = 0.01 mL, 1 cc = 1 mL) concentration: value -> mg/mL -> target (1% w/v = 10 mg/mL) molarity: mM = (mg/mL) / MW x 1000 IU to mg: mg = IU x substance factor
- Normalise to the canonical unit. The input value is multiplied by its unit's factor to reach milligrams, millilitres or milligrams per millilitre. Doing this first means every pair of units is supported without writing a factor for each pair.
- Convert out to the target unit. Divide by the target unit's factor. Because both directions use the same table, converting A to B and back to A returns the original value.
- Apply the syringe convention where relevant. Units are treated as 0.01 mL, so 30 units is 0.3 mL and 100 units is 1 mL. This is a U-100 convention and does not hold for U-40 or U-500 barrels.
- Look up the IU factor rather than deriving it. International units come from a substance-specific table, because no general relationship exists between activity and mass. A custom factor field is provided for substances the table does not carry.
- Bring in molecular weight for molarity. Milligrams per millilitre divided by molecular weight gives moles per litre, scaled to millimolar. The molecular weight field only appears in the concentration tab, since it is meaningless elsewhere.
What this method cannot tell you
- •The syringe conversion assumes a U-100 barrel. U-40 and U-500 barrels use different marks per millilitre, and applying the U-100 factor to them is a fivefold or greater error.
- •IU factors are substance-specific and revision-specific. Treat them as reference figures, not as universal constants.
- •Percentage strength is read as weight in volume. A label using volume in volume or weight in weight needs a different factor.
- •Molarity conversions use the molecular weight you supply. For a salt form, the weight of the salt and the weight of the free base give different answers.
Peptide unit converter: frequently asked questions
One thousand. One milligram is 1,000 micrograms, and one microgram is 0.001 milligrams.
- •1 mg = 1,000 mcg
- •0.5 mg = 500 mcg
- •0.25 mg = 250 mcg
- •5 mg = 5,000 mcg
One hundred, on a U-100 barrel. Each unit mark is therefore 0.01 mL, so 50 units is 0.5 mL and 10 units is 0.1 mL.
Check the barrel before relying on this. U-40 and U-500 syringes exist and use different marks per millilitre.
No. A unit is a volume marking, one hundredth of a millilitre. How much peptide sits in that volume depends entirely on the concentration of the solution.
Ten units of a 5 mg/mL solution is 500 micrograms. Ten units of a 1 mg/mL solution is 100 micrograms. Same marking, five times the difference.
Yes, exactly. A cubic centimetre and a millilitre are the same volume, and a syringe marked 1 cc holds the same as one marked 1 mL.
Multiply the IU figure by a factor specific to that substance. There is no general formula, because an international unit measures biological activity rather than mass.
- •Somatropin: about 3 IU per mg, so 1 IU is about 0.333 mg
- •Human chorionic gonadotropin: about 10,800 IU per mg, so 1 IU is about 0.0000926 mg
A 5,000 IU hCG vial therefore holds roughly 0.46 mg of protein, which is why the powder in it is barely visible.
Because hCG is potent by mass. Roughly one ten-thousandth of a gram carries about a thousand international units of activity.
This is the conversion most often got wrong by a factor of ten, and the sanity check is the vial: 5,000 IU corresponds to about half a milligram, which is consistent with how little powder a 5,000 IU vial contains.
It refers to the preservative, not the water. Bacteriostatic Water for Injection is usually 0.9 percent benzyl alcohol by weight in volume, which is 9 milligrams of benzyl alcohol per millilitre.
Multiply by ten. Percentage strength on a vial label is weight in volume, so one percent is one gram per hundred millilitres, which is ten milligrams per millilitre.
- •1% w/v = 10 mg/mL
- •0.9% w/v = 9 mg/mL
- •0.1% w/v = 1 mg/mL
Divide by the molecular weight to get moles per litre, then scale. A solution at 1 mg/mL of a 1,000 Da peptide is 1 millimolar.
Molarity counts molecules rather than mass, which is why the molecular weight is required. Two peptides at the same mass concentration are at different molar concentrations unless they weigh the same.
Whichever matches the mass you measured. If you weighed out a salt, use the salt's weight; if you are working from a net peptide content figure, use the free base.
Mixing the two is a common source of ten to twenty percent errors in molar concentration. The salt form converter shows both weights side by side.
One thousandth of a microgram, or one millionth of a milligram. Nanogram quantities appear mostly in assay work and in analytical detection limits rather than in vial labelling.
No. Mass and volume are different physical quantities, and the concentration is the bridge between them.
The converter keeps them in separate tabs for that reason. Once you have a concentration, the reconstitution calculator does the mass-to-volume step directly.
Because the value is very small or very large, and scientific notation is the only way to show it without a row of leading zeros that are easy to miscount.
A figure like 9.26e-5 mg is 0.0000926 mg. The exponent is the number of places the decimal point moves.
It formats for display at up to eight significant figures and carries full precision internally, so a conversion followed by its inverse returns the original value.
Not for the unit conversion. Those barrels carry 40 and 500 marks per millilitre respectively, so a unit is 0.025 mL and 0.002 mL rather than 0.01 mL.
The mass, volume and concentration conversions are unaffected. Only the unit-to-millilitre step assumes U-100.
Only for pure water at about four degrees Celsius, where the density is one gram per millilitre. It is a coincidence of how the units were defined, not a general rule.
For a solution containing dissolved peptide, salts or a preservative, the density is close to but not exactly one, and volume and mass are not interchangeable.
No. Every conversion runs in your browser. There is no server request, no account, and nothing is stored after you close the page.
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