Vialmetry

How Vialmetry works

Every number Vialmetry shows is arithmetic on values you entered: the vial's strength, the water you added, the syringe you use and the amounts you record. This page sets out each rule so you can check any result by hand.

What Vialmetry does not do

Vialmetry does not recommend, select or suggest an amount, a compound or a schedule, and it never fills in an amount you did not enter or choose. It is not a medical device and does not diagnose, treat, cure or prevent any medical condition. Always follow the instructions of a licensed healthcare provider and the labelling of your own products and syringes.

1. Strength after mixing

Example: a 20 mg vial with 2.0 mL of water is 10.0 mg/mL.

2. Recording what you drew (units → amount)

When you log from a mixed vial, you record the syringe mark you actually drew. Vialmetry converts it:

Insulin-style U-100 syringes hold 100 units per mL. Example: 40 units on a U-100 syringe from a 10.0 mg/mL vial is 40 ÷ 100 = 0.40 mL, and 0.40 × 10.0 = 4 mg. The logged amount is rounded to the nearest microgram (0.001 mg).

3. Converting an amount you entered (amount → units)

The exact result is always shown. The mark drawn on the syringe picture is rounded to the nearest 0.5 unit, about the finest distinction a person can read against printed graduations. The picture is a schematic, not to scale: read your own syringe, at the stopper edge nearest the needle.

4. Warnings

Warning	Rule
Over the syringe	The mark is larger than the syringe's capacity in units.
Hard to read	The mark is below 10 units. Misreading a mark by half a unit is then an error of more than 5%.
More than the vial holds	The amount is larger than the vial's strength, or than what is left in it.

5. What is left, and the use-by date

The use-by date is the mixing date plus the number of days you set (28 by default). It is your own setting, not a statement about any product's stability.

6. Checking a plan against one dilution

In Vial math you can list the amounts in your own plan. Vialmetry checks each amount at the water volume you entered and marks any that would fall outside the syringe, below 10 units, or beyond one vial.

If a different water volume would work for your whole list, it says so. It tries every volume from 0.25 mL to 10 mL in 0.25 mL steps, keeps those where every listed amount fits inside the syringe, is 10 units or more, and is within one vial, and reports the middle of that workable range, leaving headroom at both ends. It only considers amounts you listed.

7. Cost

8. Estimated level chart

For three compounds with a published half-life, Vialmetry draws an estimate from the doses you logged. Each logged dose decays by half every half-life, and the chart adds them up:

Compound	Half-life used	Source
Semaglutide	168 hours (about 1 week)	FDA prescribing information
Tirzepatide	120 hours (about 5 days)	FDA prescribing information
Retatrutide	144 hours (about 6 days)	Phase 2 trial report, NEJM 2023

The app shows the half-life, its source and a worked example from your latest dose beside the chart. The model has no absorption phase and ignores bioavailability, body weight, individual variation and interactions. It is an estimate for context, not a measurement, and no other compound gets a chart.

9. Injection-site rest

Each site's status comes from the days since you last logged it there, against the rest period you set (7 days by default):

Status	Rule
Ready	Rested for at least your rest period.
Nearly ready	Rested for two-thirds of the period, or for all but its last day, whichever comes first.
Resting	Used more recently than that.
Never used	No logged use.

An area of the body takes the status of its most recently used site. The suggested next site is a site you have never used, if there is one; otherwise the site that has rested longest. Ties go to the area of the body used least recently. These are rotation reminders, not clinical guidance.