Peptide Calculator: Reconstitution (U-100 & U-40)

What this calculator does

This peptide reconstitution calculator turns three numbers you already have into the five numbers you need at the bench. You enter the mass of peptide in the vial, the volume of bacteriostatic (BAC) water you add, and the target amount you want to measure. The calculator returns the concentration of the solution in mg/mL and mcg/mL, the draw volume in mL, the matching mark on your syringe, the micrograms contained in every 0.1 mL, and how many target amounts the vial holds.

It is a pure arithmetic tool. It does not know what compound you are working with, and it makes no assumptions about what an amount should be. It runs entirely in your browser: nothing you type is saved, logged, sent to a server or written to the page address, and your inputs disappear when you close the tab.

How to use the calculator (step by step)

Step 1 — Enter your vial size

Type the peptide mass printed on the vial label into Vial size, in milligrams. Most research vials are labelled 2 mg, 5 mg or 10 mg. Use the labelled mass, not an estimate, and if your vial's certificate of analysis reports a measured content that differs from the label, consider entering that figure instead, because the calculator can only be as accurate as the vial size you give it. The vial presets above the inputs fill in common vial sizes and water volumes for you.

Step 2 — Enter your BAC water volume

Enter the volume of bacteriostatic water you add, or plan to add, in BAC water volume, in millilitres. The quick-pick buttons set 1, 2, 3 or 5 mL in one tap. This number controls the concentration: the same vial becomes a stronger solution with less water and a weaker one with more. If you are still deciding, try a few volumes and watch the draw volume and syringe units change until they sit in a range your syringe can measure cleanly.

Step 3 — Enter your target dose

Enter the amount you want to measure in Target dose and choose mcg or mg with the unit selector next to it. The calculator converts milligrams to micrograms internally, so 2.5 mg and 2,500 mcg give identical results. Double-check the unit before you read the results: a mix-up between mg and mcg is a thousand-fold error, and it is the most common mistake people make with these calculations. The calculator never suggests an amount; it only converts the one you enter.

Step 4 — Select your syringe size

Pick your syringe from Syringe size: 0.3 mL (30 units), 0.5 mL (50 units) or 1.0 mL (100 units) on the U-100 scale, or U-40 (40 units per mL). Read the scale printed on the syringe barrel or packaging rather than assuming. The draw volume, concentration and mcg per 0.1 mL do not change with the syringe, but the unit number does, because each scale divides one millilitre into a different number of units. The gauge redraws to match the barrel you choose.

Step 5 — Read your results

The results update as you type. Concentration shows mg/mL with mcg/mL underneath. Draw volume is the volume in mL that contains your target amount. Syringe units is where that volume sits on your chosen scale, and the gauge shows the same mark visually. mcg per 0.1 mL describes the solution itself, and Doses per vial is how many times the target fits in the vial. Use Copy result to paste a plain-text summary into your lab notes.

The reconstitution formulas, written out

Every number on this page comes from five short formulas. We publish them so you can check any result by hand. The worked example throughout uses a 5 mg vial, 2 mL of BAC water and a 250 mcg target amount.

Concentration

Worked example: 5 mg ÷ 2 mL = 2.5 mg/mL, which is 2.5 × 1,000 = 2,500 mcg/mL. Concentration tells you how much peptide each millilitre of solution carries. It is fixed once the water is added and changes only if you add more diluent.

Draw volume

Worked example: 250 mcg ÷ 2,500 mcg/mL = 0.1 mL. Draw volume is the physical amount of liquid that contains your target. It is the most fundamental result, because every syringe scale is simply a different way of marking the same volume.

Syringe units

A U-100 syringe has 100 units per mL; a U-40 syringe has 40. Worked example: 0.1 mL × 100 = 10 units on any U-100 syringe, and 0.1 mL × 40 = 4 units on a U-40 syringe. The volume is identical; only the label on the barrel differs.

mcg per 0.1 mL

Worked example: 2,500 × 0.1 = 250 mcg in every 0.1 mL. This is a property of the solution, so it does not depend on which syringe you use. It is the most portable way to write down what is in a vial.

Doses per vial

Worked example: 5 × 1,000 ÷ 250 = 20. This is an arithmetic ceiling. Real-world handling losses in the needle hub, on the vial walls and from air bubbles mean the practical number is usually a little lower.

How to read a syringe

Insulin-style syringes are marked in "units" rather than millilitres, and the size of a unit depends on the syringe's scale. The scale is printed on the barrel or the packaging, usually as U-100 or U-40, and it is the single most important thing to check before you trust any unit number, including the ones this calculator gives you.

U-100 syringes (100 units per mL)

A U-100 syringe divides one millilitre into 100 units, so each unit is 0.01 mL. They come in three common barrel sizes: 0.3 mL (30 units), 0.5 mL (50 units) and 1.0 mL (100 units). On a 1.0 mL barrel each small tick is usually 2 units; on 0.3 mL and 0.5 mL barrels ticks are often single units, and some 0.3 mL barrels add half-unit marks. A 0.1 mL draw is 10 units on every U-100 barrel. Smaller barrels are easier to read precisely for small volumes because the same volume spreads over a longer length of barrel.

U-50 syringes (50 units per mL)

U-50 syringes divide one millilitre into 50 units, so each unit is 0.02 mL, twice the volume of a U-100 unit. They are less common, but you will see the scale on some barrels sold for specific insulin types. A 0.1 mL draw is 5 units on a U-50 scale. This calculator does not list U-50 as a menu option, but the rule is the same: multiply the draw volume in mL by 50. If you use U-50 syringes, take the draw volume from the calculator and apply that multiplication.

U-40 syringes (40 units per mL)

U-40 syringes divide one millilitre into 40 units, so each unit is 0.025 mL. They are made for U-40 insulin, which is common in veterinary use, and they turn up in general supply channels, which is why confusing them with U-100 syringes is a real risk. A full U-40 barrel is 40 units, and the calculator's U-40 gauge marks a tick every 2 units with labels every 10. A 0.1 mL draw is 4 units on a U-40 scale, not 10.

Why the same draw volume gives different unit numbers

The rule is simple: units = draw volume in mL × units per mL of the syringe. A unit is not a fixed amount of anything; it is one division of a particular scale. A U-100 barrel has 100 divisions per millilitre and a U-40 barrel has 40, so a U-40 unit holds 2.5 times as much liquid as a U-100 unit. The same physical 0.1 mL therefore reads as 10 units on a U-100 barrel and as a smaller number, 4 units, on a U-40 barrel. If you draw "10 units" on a U-40 syringe when the figure was calculated for U-100, you have drawn 0.25 mL, two and a half times the intended volume.

Reading the barrel: where the plunger tip sits, not where the liquid ends

Read the volume at the leading edge of the plunger's rubber stopper, the flat ring that touches the liquid, not at the far end of the stopper and not at the trailing edge of the liquid or an air bubble. Hold the syringe at eye level and needle up, tap out any air bubbles, and push them out before reading. A bubble takes up space in the barrel, so a reading taken with air inside will contain less solution than the mark suggests.

How to use the reconstitution chart

The chart in the calculator above shows, for the vial size you enter, how 1, 2, 3 and 5 mL of BAC water change the concentration, the micrograms in each 0.1 mL, and the units that hold 250 mcg on both a U-100 and a U-40 scale. It is calculated with exactly the same formulas as the main results, so it updates as soon as you change the vial size. With JavaScript turned off, it shows the default 5 mg vial. Use it to choose a water volume that keeps your draws in a comfortable, measurable range: generally not below a couple of units, and not above one barrel.

Why mcg per 0.1 mL matters more than syringe units

Syringe units are a property of the syringe, not of the solution. The same vial, mixed the same way, reads as 10 units on a U-100 barrel and 4 units on a U-40 barrel. If you write "10 units" in your notes and later pick up a different syringe, or someone else reads your notes, that number is ambiguous at best and dangerous at worst.

mcg per 0.1 mL is a property of the solution itself. It says how much peptide is in a fixed physical volume, so it stays the same whatever you measure with: a U-100 barrel, a U-40 barrel, a graduated pipette or a lab balance. That makes it the stable number to label a vial with and to record in your notes, alongside the vial size and the volume of water you added.

PeptideChecked reports mcg per 0.1 mL next to syringe units for this reason. Many popular calculators stop at concentration and syringe units, which leaves you translating between scales by hand. If you record one number from this page, make it mcg per 0.1 mL.

Common reconstitution mistakes

Mistake 1 — Confusing mg and mcg

One milligram is 1,000 micrograms. Typing 250 into the target field with mg selected instead of mcg asks for a thousand times more than intended, and the calculator will dutifully report a draw volume larger than the whole vial. Vial labels are usually in mg while research amounts are often discussed in mcg, which is exactly where the mix-up happens. Always check the unit selector before reading results, and sanity-check that the draw volume is smaller than the water you added.

Mistake 2 — Assuming every syringe is U-100

Assuming every insulin-style syringe is U-100 is the single most common unit error in reconstitution arithmetic. A U-40 barrel reads 40 units per mL, not 100, so each U-40 unit holds 2.5 times more liquid. A number calculated for U-100 and drawn on a U-40 syringe delivers 2.5 times the intended volume. Read the scale printed on the barrel or packaging, select the matching option in the calculator, and never mix syringes from different boxes without checking both.

Mistake 3 — Adding BAC water to the wrong mark

The concentration is only correct if you actually added the volume you entered. Drawing water to the wrong line, for example reading a 1.0 mL barrel as if it were a 0.5 mL barrel, or counting units as tenths of a millilitre, silently changes every result on the page. Measure the diluent with a syringe or pipette whose scale you have confirmed, add it once, and write the volume on the vial label along with the date so the number you enter later matches reality.

Mistake 4 — Spraying BAC water directly onto the powder

Lyophilised peptide is a fragile freeze-dried cake. Standard laboratory practice is to run the diluent slowly down the inside wall of the vial rather than jetting it straight onto the powder, then let it dissolve and swirl gently instead of shaking. Harsh handling can cause foaming and can damage some peptides. This does not change the arithmetic, but it affects whether the material in the vial matches what the label and the calculator assume.

Mistake 5 — Reusing a vial past its documented stability window

Reconstituted peptides are generally less stable than the dry powder, and stability varies by compound, diluent and storage temperature. The calculator assumes the vial still contains its full labelled content. If a solution has been stored longer than its supplier or the literature documents, or kept at the wrong temperature, the true concentration may be lower than the number on your screen. Label every vial with its reconstitution date and follow the storage guidance for that specific material.

Mistake 6 — Trusting a vendor's "dosing chart" over your own arithmetic

Some vendor sites publish charts that pair their products with specific amounts or schedules. Beyond the regulatory problems that creates, these charts assume a vial size, water volume and syringe scale that may not match yours. Always calculate from your own numbers: the vial size on your label (or measured content on your COA), the water you actually added, and the scale printed on your syringe. The math is the same five formulas above, and it takes seconds to verify.

How to verify the peptide you are reconstituting

A calculator is only as accurate as the vial size you type in, and that number is only as trustworthy as the vendor behind it. Before you rely on any label, check four things. First, a public certificate of analysis (COA) that matches your vial's lot number and reports both purity and measured content; our guide on how to read a peptide COA walks through what to look for. Second, a named third-party lab on that COA, so the result can be traced to an organisation rather than an anonymous PDF. Third, independent test data from services such as Finnrick, which buys and tests products without the vendor's involvement; see Janoshik vs Finnrick testing for how the two differ. Fourth, the vendor's FDA record, including any warning letters.

Our research peptide vendor reviews check each of those signals and disclose what we find, including red flags. For vendors that publish lot-level results, see our list of third-party tested peptides, and for the full US ranking with every vendor's strengths and weaknesses, see our guide to the best place to buy peptides online.

Accuracy and methodology

The calculator uses exactly the five formulas shown above, with no compound-specific adjustments. Inputs are normalised first: the target amount is converted to micrograms if you enter it in milligrams, and each syringe option carries its own units-per-mL value (100 for the three U-100 barrels, 40 for U-40), so the U-40 result goes through the same formula as the U-100 results.

Results are rounded for display only, never during calculation: concentration to 3 decimal places in mg/mL and 1 in mcg/mL, draw volume to 3 decimal places, syringe units to 1, mcg per 0.1 mL to 1, and doses per vial to 1, with trailing zeros removed. If any input is zero or blank the calculator shows a dash rather than a misleading number, and it warns you when a draw is larger than one barrel or smaller than one unit, the point at which insulin-style syringes stop being readable with any accuracy.

There are things it cannot account for. It does not model vial overfill or underfill, the dead volume held in a needle hub, liquid lost on the vial walls, or the small volume the dissolved powder itself adds to the solution. It assumes the vial contains exactly the mass you enter. Measured volumes should be verified against a calibrated instrument wherever precision matters.

Above all, the calculator does not tell anyone what to take, how often, or whether any compound is appropriate for any purpose. It converts units. The same research-first approach applies across the site; see how we score vendors.

Frequently asked questions

Research use only

For the current regulatory picture, including FDA's compounding categories and recent warning letters, see FDA peptide regulation in 2026.