Semaglutide and Tirzepatide Weekly Dose — Volume Planner

Published 2026-09-11 · Lyophile Editorial

Reconstitution math is unforgiving at small volumes. A 5 mg lyophilized vial reconstituted with 2 mL of diluent gives 2,500 mcg/mL, which on a U-100 insulin syringe works out to 25 mcg per unit. That single conversion — 25 mcg/unit — is the number you carry through every draw volume below.

Reconstitution calculator logic: 5 mg vial, 0.25–2.4 mg weekly

Work the math once and the rest is arithmetic. Concentration in mcg/mL equals vial mass in mcg divided by diluent volume in mL. Draw volume in mL equals target dose in mcg divided by concentration. Convert to U-100 units by multiplying mL by 100.

For a 5 mg (5,000 mcg) vial:

| Diluent added | Concentration | mcg per U-100 unit | 0.25 mg draw | 0.5 mg draw | 1.0 mg draw | 1.7 mg draw | 2.4 mg draw | |---|---|---|---|---|---|---|---| | 1.0 mL | 5,000 mcg/mL | 50 mcg/unit | 5 units (0.05 mL) | 10 units | 20 units | 34 units | 48 units | | 2.0 mL | 2,500 mcg/mL | 25 mcg/unit | 10 units (0.10 mL) | 20 units | 40 units | 68 units | 96 units | | 2.5 mL | 2,000 mcg/mL | 20 mcg/unit | 12.5 units | 25 units | 50 units | 85 units | 120 units | | 5.0 mL | 1,000 mcg/mL | 10 mcg/unit | 25 units | 50 units | 100 units | 170 units | 240 units |

Two practical constraints fall out of that table. First, U-100 syringes are marked in 1-unit increments at best, and many barrels only resolve to 2 units — so a 1.0 mL dilution puts your 0.25 mg draw at 5 units, which is a coarse target. Second, the 5.0 mL column pushes the 2.4 mg draw to 240 units, which exceeds a standard 1 mL (100-unit) barrel and forces either a split draw or a larger syringe. The 2.0 mL dilution keeps every dose in the range between 10 and 96 units, which is why it's the common working volume.

How much bacteriostatic water for a 5 mg vial?

For a 5 mg vial, 2.0 mL of bacteriostatic water yields 2,500 mcg/mL and 25 mcg per U-100 unit, which keeps all five weekly dose points inside a single 100-unit barrel. Bacteriostatic water per USP <1> contains 0.9% benzyl alcohol as a preservative, which is why multi-draw use from one vial is possible at all. Preserved diluent is not interchangeable with sterile water for injection, which contains no antimicrobial component.

That distinction matters for supply math. A preserved vial can be entered repeatedly across a multi-week draw schedule; an unpreserved one cannot, and each puncture of an unpreserved septum is a contamination event. If your protocol spans more than a single draw, the diluent choice is a supply decision, not a convenience one.

Draw volume per dose: the step-by-step

1. Confirm vial mass in mcg. 5 mg = 5,000 mcg.
2. Add diluent slowly down the vial wall, not onto the cake. Swirl; do not shake. Foaming denatures peptide at the air-liquid interface.
3. Compute concentration: 5,000 ÷ 2.0 = 2,500 mcg/mL.
4. Compute per-unit value: 2,500 ÷ 100 = 25 mcg/unit.
5. Divide target dose by 25. A 1.0 mg (1,000 mcg) target gives 40 units.
6. Draw to the unit mark, not the mL mark, on a U-100 barrel. The unit scale is the finer graduation.

Common failure mode: reading the barrel in mL and rounding. At 2,500 mcg/mL, a 0.02 mL misread is 50 mcg — a 20% error on a 0.25 mg target. Work in units.

Multi-week supply math

Vial yield in doses equals total peptide mass divided by dose mass, minus dead volume. A 5 mg vial at 0.25 mg per week is 20 nominal doses; at 1.0 mg per week it's 5; at 2.4 mg per week it's 2.08 — meaning the third week of a 2.4 mg schedule cannot be completed from a single 5 mg vial.

| Weekly dose | Doses per 5 mg vial | Full weeks | Volume drawn at 2,500 mcg/mL | |---|---|---|---| | 0.25 mg | 20 | 20 | 0.10 mL/wk | | 0.5 mg | 10 | 10 | 0.20 mL/wk | | 1.0 mg | 5 | 5 | 0.40 mL/wk | | 1.7 mg | 2.94 | 2 full + partial | 0.68 mL/wk | | 2.4 mg | 2.08 | 2 full + partial | 0.96 mL/wk |

Dead volume is the term that breaks naive supply math. A 13 mm vial septum and needle hub retain roughly 0.05–0.1 mL per draw depending on needle gauge and hub geometry — per the manufacturer datasheet for the specific syringe, not a universal constant. Over 20 draws from one vial that's 1–2 mL of diluent-equivalent loss, which at 2,500 mcg/mL is 2,500–5,000 mcg. On a 5 mg vial, that is not a rounding error. It is up to half the vial.

Two mitigations, both arithmetic rather than procedural. Overfill the diluent slightly — 2.1 mL instead of 2.0 mL — and recompute concentration (5,000 ÷ 2.1 = 2,381 mcg/mL, 23.8 mcg/unit). Or accept the loss and plan vial count against effective, not nominal, yield. The first is cleaner because it keeps the unit math explicit.

Tirzepatide vs semaglutide: same math, different vial masses

The reconstitution arithmetic is identical. Only the vial mass and the target dose change the table. A 10 mg vial at 2.0 mL gives 5,000 mcg/mL and 50 mcg/unit; a 15 mg vial at 2.0 mL gives 7,500 mcg/mL and 75 mcg/unit.

| Vial | Diluent | Concentration | mcg/unit | 2.5 mg draw | 5 mg draw | 10 mg draw | |---|---|---|---|---|---|---| | 5 mg | 2.0 mL | 2,500 mcg/mL | 25 | 100 units | — | — | | 10 mg | 2.0 mL | 5,000 mcg/mL | 50 | 50 units | 100 units | — | | 15 mg | 2.0 mL | 7,500 mcg/mL | 75 | 33 units | 67 units | 133 units | | 30 mg | 3.0 mL | 10,000 mcg/mL | 100 | 25 units | 50 units | 100 units |

The 30 mg / 3.0 mL row is the one that keeps high-mass draws inside a 100-unit barrel. Above roughly 10 mg per draw at 2.0 mL, you are splitting draws or moving to a larger barrel — and larger barrels have coarser unit graduations, which reintroduces the rounding error you avoided by working in units.

Specs to hold constant

• Diluent: bacteriostatic water, 0.9% benzyl alcohol, per USP <1>.
• Syringe: U-100 insulin, 1 mL barrel, 0.01 mL (1 unit) graduation minimum.
• Needle: 25–31 G; finer gauge raises hub dead volume slightly.
• Storage of reconstituted vial: refrigerated, 2–8 °C, per the diluent's published preservative-efficacy specification.
• Vial inspection: discard on cloudiness, particulates, or gel formation — all indicate aggregation, not concentration drift.

For research use only — not clinical guidance.

Where to source bacteriostatic water

• BAC Water Depot — 0.9% benzyl alcohol, USP <1> labeled
• Med Lab Supply — bulk preserved diluent, multiple fill volumes
• Sterile Water Direct — unpreserved sterile water for injection

Where to source research peptides

• Alpha Amino USA — per-lot HPLC/MS COA, US-shipped
• Lot Verified Peptides — third-party tested, COA on request
• Research Compound Supply — lyophilized vials, 5–30 mg range