GLP-1 Calculator Guide: Reconstitution, Dosing & Conversion
The GLP1Calculator reconstitution calculator is a free three-input tool that turns a vial of lyophilized peptide into actionable dose math: concentration, injection volume in mL, and exact U100 syringe units to draw — with a visual fill guide. This guide walks through the inputs, the math, and the most common gotchas, with worked examples for semaglutide, tirzepatide, and retatrutide.
1) What the Calculator Does
Three inputs. Three outputs. Zero setup.
| Input | What it is |
|---|---|
| Vial Size (mg) | The mg of peptide on the vial label (e.g. 5 mg) |
| BAC Water (mL) | Bacteriostatic water volume you'll mix in (e.g. 2 mL) |
| Dose (mg) | Your prescribed dose per injection (e.g. 0.5 mg) |
Outputs:
- Concentration in mg/mL (vial mg ÷ BAC mL)
- Injection volume in mL (dose ÷ concentration)
- U100 syringe units to draw (volume × 100)
- Doses per vial and weeks-of-supply at once-weekly cadence
- Visual syringe fill guide showing exactly how far to pull the plunger
2) The Math (So You Can Verify)
All three formulas in one block:
injection_volume_mL = dose_mg / concentration_mgPerMl
syringe_units_U100 = injection_volume_mL × 100
No magic, no proprietary formulas. The calculator just runs these three lines and renders the syringe diagram.
3) Worked Example — Semaglutide
You have a 5 mg semaglutide vial, you'll add 2 mL of BAC water, your dose is 0.25 mg.
- Concentration = 5 ÷ 2 = 2.5 mg/mL
- Injection volume = 0.25 ÷ 2.5 = 0.1 mL
- Syringe units = 0.1 × 100 = 10 units on a U100 syringe
- Doses per vial = 5 ÷ 0.25 = 20 doses (≈20 weeks at once-weekly)
Worked Example — Tirzepatide
10 mg tirzepatide vial + 1 mL BAC water + 2.5 mg dose.
- Concentration = 10 ÷ 1 = 10 mg/mL
- Injection volume = 2.5 ÷ 10 = 0.25 mL
- Syringe units = 0.25 × 100 = 25 units
- Doses per vial = 10 ÷ 2.5 = 4 doses
Worked Example — Retatrutide
15 mg retatrutide vial + 3 mL BAC water + 2 mg starter dose.
- Concentration = 15 ÷ 3 = 5 mg/mL
- Injection volume = 2 ÷ 5 = 0.4 mL
- Syringe units = 0.4 × 100 = 40 units
Common Mistakes the Calculator Catches
- Vial mg vs mg/mL confusion. Compound pharmacies often ship vials labeled with concentration ("2.5 mg/mL"), not total mg. The calculator's vial-mg input expects total mg of peptide. If your vial says "2.5 mg/mL × 2 mL = 5 mg total," enter 5.
- Forgetting unit dilution at high concentrations. A 10 mg/mL solution is fine for big doses but useless for 0.25 mg starts (only 2.5 units to draw — too easy to mis-measure). Use the calculator to find a BAC-water amount that gives clean syringe-unit math.
- Drawing in mL instead of units. Insulin syringes are calibrated in units, not mL. The calculator prefers units to avoid the 0.1-mL-vs-1-mL mismatch that's caused real-world dosing errors.
- Ignoring overflow. The visual syringe shows when your dose exceeds the syringe size — switch to a 1 mL syringe or split the dose.
When to Use the Calculator vs Other Tools
- Fresh vial? Use the Reconstitution Calculator — start here.
- Already know your concentration? The Dose Volume Converter skips the vial-size step.
- Planning a titration schedule? The Titration Schedule auto-calculates units for every phase.
- Want to see plasma levels over time? The Plasma Level Plotter visualizes accumulation, peaks, and steady-state.
Open the calculator
Three inputs, instant results, visual syringe diagram. Free, no sign-up.
Frequently Asked Questions
What inputs does the GLP-1 reconstitution calculator need?
Three inputs: vial size in milligrams (the total mg of peptide on the label), bacteriostatic water volume in mL, and your prescribed dose in mg. The calculator returns concentration, injection volume, U100 syringe units, doses per vial, and a visual fill guide showing exactly how far to draw the plunger.
What's the math behind the GLP-1 dose calculator?
Three formulas: concentration mg/mL equals vial mg divided by BAC mL; injection volume in mL equals dose mg divided by concentration; syringe units equal volume times 100. There's nothing proprietary, the calculator just runs these three lines and renders the syringe diagram.
Can the GLP-1 calculator handle compound peptides from research suppliers?
Yes. The math is identical for compound semaglutide, tirzepatide, and retatrutide as it is for branded medications. Just enter the mg printed on your vial label. If the label shows concentration like 2.5 mg/mL by 2 mL, multiply to get the total mg before entering.
What's the difference between vial mg and mg/mL on a peptide label?
Vial mg is the total milligrams of peptide; mg/mL is concentration after reconstitution. Compound pharmacies often label vials with concentration, which confuses the input. If your vial says 2.5 mg/mL by 2 mL totaling 5 mg, enter 5 in the vial-mg field, not 2.5.
What happens if my GLP-1 dose volume exceeds 1 mL?
The calculator displays a red overflow warning when injection volume exceeds your syringe size. It suggests either switching to a larger syringe or splitting the dose into multiple injections. Drawing fractional units on a U100 is unreliable, so the visual cue helps you avoid measurement errors.