What syringe size should I use for GLP-1 injections?

U-100 insulin syringes are standard for reconstituted peptides. Common sizes: 0.3mL (30 units) for small doses, 0.5mL (50 units) for moderate doses, and 1.0mL (100 units) for larger doses. Smaller syringes provide more precise measurements for low doses.

GLP-1 Dose Calculator

Calculate syringe units for reconstituted semaglutide, tirzepatide, and other GLP-1 peptides. Includes a dose conversion chart for switching between medications.

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Medical Disclaimer: This calculator is for informational and educational purposes only. It is not medical advice. Always consult your healthcare provider before starting, adjusting, or switching any GLP-1 medication. Dosing decisions must be made by a qualified clinician.

Reconstitution Dose Calculator

Calculate how many units to draw on your insulin syringe for reconstituted GLP-1 peptides (semaglutide, tirzepatide, retatrutide).

Vial Size (Presets)

Vial Contents (mg) BAC Water Added (mL)

Syringe Size Desired Dose (mg)

Common Dose Presets

GLP-1 Dose Conversion Chart

Approximate clinical equivalences for switching between GLP-1 receptor agonists. These are not direct mg-to-mg conversions — each medication has unique potency, receptor targets, and pharmacokinetics.

Table 1: Approximate GLP-1 dose equivalences (not FDA-approved conversions)
Semaglutide Ozempic / Wegovy	Tirzepatide Mounjaro / Zepbound	Liraglutide Saxenda / Victoza	Dulaglutide Trulicity	Phase
0.25 mg/wk	2.5 mg/wk	0.6 mg/day	0.75 mg/wk	Initiation
0.5 mg/wk	2.5–5 mg/wk	1.2–1.8 mg/day	1.5 mg/wk	Titration
1.0 mg/wk	5.0 mg/wk	1.8 mg/day	1.5–3.0 mg/wk	Titration
1.7 mg/wk	7.5–10 mg/wk	2.4–3.0 mg/day	3.0–4.5 mg/wk	Maintenance
2.4 mg/wk	10–15 mg/wk	3.0 mg/day	4.5 mg/wk	Max dose

Quick Reference: Reconstitution Units

Common vial/BAC water combinations and the units to draw for typical semaglutide doses (U-100 syringe).

Table 2: Units to draw on U-100 syringe by vial size and BAC water volume
Vial + Water	Concentration	0.25 mg	0.5 mg	1.0 mg	2.0 mg	2.5 mg
5 mg + 1 mL	5.0 mg/mL	5 u	10 u	20 u	40 u	50 u
5 mg + 2 mL	2.5 mg/mL	10 u	20 u	40 u	80 u	100 u
10 mg + 1 mL	10.0 mg/mL	2.5 u	5 u	10 u	20 u	25 u
10 mg + 2 mL	5.0 mg/mL	5 u	10 u	20 u	40 u	50 u
15 mg + 3 mL	5.0 mg/mL	5 u	10 u	20 u	40 u	50 u

Formula: Units = (Dose ÷ Concentration) × 100. Use a 0.3 mL syringe for doses ≤ 5 units for best accuracy.

Titration Schedules

Semaglutide (Ozempic / Wegovy)

Weekly SC injection. Titrate every 4 weeks:
0.25 mg → 0.5 mg → 1.0 mg → 1.7 mg → 2.4 mg (max)

Tirzepatide (Mounjaro / Zepbound)

Weekly SC injection. Titrate every 4 weeks:
2.5 mg → 5 mg → 7.5 mg → 10 mg → 12.5 mg → 15 mg (max)

Liraglutide (Saxenda / Victoza)

Daily SC injection. Titrate weekly:
0.6 mg → 1.2 mg → 1.8 mg → 2.4 mg → 3.0 mg (max for weight loss)

Dulaglutide (Trulicity)

Weekly SC injection. Titrate every 4 weeks:
0.75 mg → 1.5 mg → 3.0 mg → 4.5 mg (max)

Switching Between GLP-1 Medications

Switching requires medical supervision. Below are general principles from published clinical guidance.

From Semaglutide → Tirzepatide

•Wait 7 days after last semaglutide injection (half-life ~7 days).
•Most guidelines recommend starting at 2.5 mg tirzepatide regardless of previous semaglutide dose.
•Some clinicians start at 5 mg for patients who tolerated semaglutide 1.0+ mg without GI issues.
•Titrate every 4 weeks based on tolerability and efficacy.

From Tirzepatide → Semaglutide

•Wait 7 days after last tirzepatide injection (half-life ~5 days).
•Start semaglutide at 0.25 mg and follow standard titration schedule.
•Patients may initially experience less appetite suppression until semaglutide reaches therapeutic dose.

From Daily → Weekly GLP-1

•Start the weekly injection the day after the last daily dose.
•For patients on max daily dose (liraglutide 1.8 mg), start semaglutide at 0.5 mg or tirzepatide at 5 mg.

From Oral Semaglutide (Rybelsus) → Injectable

•Patients on oral semaglutide 14 mg/day can switch to SC semaglutide 0.5 mg/wk or tirzepatide 5 mg/wk.
•Start the injection the day after the last oral dose.

Important: Never switch medications without consulting your prescribing clinician. Individual dosing depends on indication (T2D vs weight loss), tolerability, lab results, and clinical response. These guidelines are generalizations from published research.

How the GLP-1 Dose Calculator Works

The reconstitution calculator uses a simple 3-step formula to convert your desired dose in milligrams to units on an insulin syringe:

Step 1: Concentration (mg/mL) = Vial Contents (mg) ÷ BAC Water (mL)

Step 2: Volume to Draw (mL) = Desired Dose (mg) ÷ Concentration (mg/mL)

Step 3: Syringe Units = Volume (mL) × 100 (for U-100 syringes)

Example: A 5 mg vial reconstituted with 2 mL BAC water gives a concentration of 2.5 mg/mL. For a 0.25 mg dose: 0.25 ÷ 2.5 = 0.1 mL = 10 units on a U-100 syringe.

Understanding GLP-1 Receptor Agonists

GLP-1 (glucagon-like peptide-1) receptor agonists are a class of medications used for type 2 diabetes and weight management. They mimic the natural GLP-1 hormone, which stimulates insulin release, suppresses appetite, and slows gastric emptying. Key medications include:

•Semaglutide (Ozempic, Wegovy, Rybelsus) — Pure GLP-1 agonist; weekly injection or daily oral tablet.
•Tirzepatide (Mounjaro, Zepbound) — Dual GLP-1/GIP agonist; weekly injection; generally more potent for weight loss.
•Liraglutide (Saxenda, Victoza) — GLP-1 agonist; daily injection; shorter half-life than semaglutide.
•Dulaglutide (Trulicity) — GLP-1 agonist; weekly injection; primarily for type 2 diabetes.

Why Nutrition Matters on GLP-1 Medications

GLP-1 medications reduce appetite significantly, which makes it critical to prioritize nutrient-dense food within smaller portions. Key nutritional priorities while on GLP-1 therapy:

1.High protein: Aim for 1.2–1.6 g/kg body weight to prevent muscle loss during weight reduction.
2.Adequate hydration: GLP-1 medications can cause nausea; staying hydrated helps manage side effects.
3.Fiber intake: Supports digestion slowed by GLP-1 activity; prevents constipation.
4.Micronutrients: With reduced food intake, every meal must count — focus on vitamins and minerals.

Use our GLP-1 calorie calculator to find your optimal daily calories and protein while on these medications, or get a personalized GLP-1 meal plan with high-protein, nutrient-dense meals.

Key Takeaways

Dose formula: Units = (Dose mg ÷ Concentration mg/mL) × 100
There is no direct mg-to-mg conversion between different GLP-1 medications.
When switching, most guidelines recommend starting at the lowest dose of the new medication.
Tirzepatide is a dual GLP-1/GIP agonist — more potent per mg than semaglutide alone.
Always titrate gradually (every 4 weeks) to minimize GI side effects.
Prioritize protein (1.2–1.6 g/kg) to preserve muscle mass during GLP-1 weight loss.

What is a GLP-1 dose calculator?

A GLP-1 dose calculator helps you determine exactly how many units to draw from an insulin syringe when using reconstituted peptide medications. It calculates injection volume based on your vial contents, diluent amount, and prescribed dose in milligrams. This is essential for compounded peptides that require manual reconstitution.

How do I calculate my semaglutide dose?

Enter your vial size (e.g., 5 mg or 10 mg), the amount of bacteriostatic water used for reconstitution, select your syringe size, and enter your prescribed dose. The calculator converts this to syringe units. For example: 5 mg vial + 2 mL water = 2.5 mg/mL concentration. A 0.5 mg dose = 20 units.

How do I convert semaglutide to tirzepatide doses?

There is no direct mg-to-mg conversion. Approximate clinical equivalences: Semaglutide 0.5 mg ≈ Tirzepatide 2.5–5 mg; Semaglutide 1.0 mg ≈ Tirzepatide 5 mg; Semaglutide 2.4 mg ≈ Tirzepatide 10–15 mg. However, most clinicians recommend restarting at the lowest dose (2.5 mg tirzepatide) when switching, regardless of previous semaglutide dose.

What is peptide reconstitution?

Reconstitution is mixing lyophilized (freeze-dried) peptide powder with bacteriostatic water to create an injectable solution. The concentration depends on how much diluent you add. More water means lower concentration and more units per dose. Once reconstituted, vials must be refrigerated (2–8°C) and typically last 28–60 days.

How much bacteriostatic water should I use?

Common amounts are 1–2 mL per vial. Less water = higher concentration = fewer units per dose. More water = lower concentration = more units per dose but easier to measure small doses. For precision with low doses (0.25 mg), using 2 mL of water with a small syringe (0.3 mL) provides the most accurate measurements.

Can I switch from Ozempic to Mounjaro?

Switching should only be done under medical supervision. General guidance: stop semaglutide, wait 7 days, then start tirzepatide at 2.5 mg weekly. Titrate every 4 weeks. Some patients switching from semaglutide 1.0+ mg may start at 5 mg tirzepatide if they had good GI tolerance. Never overlap these medications.

What syringe size should I use?

U-100 insulin syringes are standard for reconstituted peptides. For doses requiring fewer than 30 units, use a 0.3 mL syringe for maximum precision. For doses of 30–50 units, use a 0.5 mL syringe. For doses above 50 units, use a 1.0 mL syringe. Smaller syringes have finer markings, making small doses easier to read accurately.

Is this calculator for Ozempic or Wegovy pens?

No. Pre-filled pens (Ozempic, Wegovy, Mounjaro, Zepbound) have fixed concentrations with built-in dosing dials — no calculation is needed. This calculator is specifically for reconstituted compounded peptides from vials that require manual dose calculation with insulin syringes.

Sources & Accuracy

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Is this information reliable?

This calculator uses a standard pharmacological formula (Dose ÷ Concentration × 100) that is universally accepted for reconstituted injectable medications. The dose equivalence chart is derived from FDA prescribing information, peer-reviewed clinical trials, and published switching guidelines. However, no dose equivalence table is FDA-approved — all comparisons are clinical estimates that vary by individual.

Last reviewed: June 2026

Medical review: Content informed by published prescribing information and clinical guidelines

Limitations: Not for pre-filled pens; does not account for individual absorption or compounding variability

References

Novo Nordisk. Wegovy (semaglutide) Prescribing Information. FDA, revised 2024. FDA label
Eli Lilly. Mounjaro (tirzepatide) Prescribing Information. FDA, revised 2024. FDA label
Frías JP, et al. (2021). Tirzepatide versus semaglutide once weekly in patients with type 2 diabetes. New England Journal of Medicine, 385:503-515. DOI
Jastreboff AM, et al. (2022). Tirzepatide once weekly for the treatment of obesity. New England Journal of Medicine, 387:205-216. DOI
Practical guide: GLP-1 and dual GLP-1RA/GIP receptor agonists in diabetes mellitus. World Journal of Diabetes, 2024. PMC 10999055
Wisconsin Academy of Family Physicians. GLP-1RA Dose Comparisons Chart. Updated 2024. WAFP
The Pharmaceutical Journal (2024). Switching between weight-loss medications. PJ article

Editorial Note: This tool provides general dosing information only. It is not a substitute for professional medical advice. GLP-1 medication dosing is complex and must be individualized by a licensed healthcare provider. Compounded peptides may have different purity, potency, and stability compared to brand-name products. Always verify your concentration and dose with your prescribing clinician or pharmacist.