The human version, firstThe vial says milligrams. The dose people talk about is in micrograms, or in fractions of a milligram. The syringe is marked in units, which are neither. Three systems, one kitchen counter, and a thousand-fold mistake sitting between two of them. This does the conversion, tells you when the number lands between tick marks, and tells you when you have added so little water that the dose is too small to measure well. It does not tell you what to take. Nothing on this site does.
Why the charts you find don't fit
Charts assume a vial and a water volume. Reconstitute a 10 mg tirzepatide vial with 2 mL and 1.25 mg is 25 units; with 1 mL it is 12.5, which no 1 mL syringe can read cleanly. GHK-Cu comes in 100 mg vials that most calculators refuse to handle sensibly. Semaglutide doses are small enough that a little water makes the difference between a readable 10 units and an unreadable 2.5. None of that is on a chart someone screenshotted from a forum. All of it is in the tool above.
The three things it will stop you on
Under five units. Measurement error gets large. It tells you how much water makes the same dose readable. Over the syringe's capacity. A 0.3 mL syringe stops at 30 units; it says so and suggests the fix. Between the marks. A 1 mL syringe reads in two-unit steps; when your dose lands on an odd number it names the nearest marks and the smaller syringe that reads it exactly.
Keep it on your phone
The same engine runs at Vial Tool as a free app you can add to your home screen — it works with no signal, and it saves your setups on the device without an account. Compound-specific printable charts live there too: tirzepatide, semaglutide, retatrutide, GHK-Cu, BPC-157, and a plain guide to which insulin syringe reads what.
What this is not
A recommendation. The quick-fill amounts are numbers people commonly search for, labelled as such. Whether any compound belongs in your protocol, at what amount, alongside the HRT or thyroid medication or contraception you may already take, is a conversation with a clinician who knows your history — we wrote down the questions to bring. The calculator's only job is to make sure that whatever number you were given ends up on the syringe correctly.