Semaglutide mg to Units: A Complete Conversion Guide

If you've been prescribed compounded semaglutide, you've probably felt this confusion: the bottle is labeled in milligrams per milliliter (for example, "5 mg/mL"), your prescriber wrote a dose in milligrams (for example, "0.25 mg weekly"), and the syringe in your sharps kit is marked in units. Three different units of measurement, no conversion chart on the label. The result: an unnecessary amount of math in a bathroom at 7 a.m.

This guide fixes that. We will walk through the math in about 30 seconds, give you a reference table you can screenshot, then cover the five conversion mistakes that pharmacists see most often. If you prefer to skip the reading, use the converter, but the background is worth 10 minutes for anyone planning to use semaglutide long-term.

Why conversion exists

Branded semaglutide comes in a pre-filled pen — Wegovy, Ozempic, Rybelsus. You dial the pen to a milligram dose, or you take a fixed-dose tablet. There is no math. Compounded semaglutide, sold by 503A and 503B pharmacies, is different. It is dispensed as a multi-dose vial with a printed concentration (commonly 2.5, 5, or 10 mg/mL), and patients draw each dose themselves using an insulin-style syringe marked in units. The system borrows the insulin syringe because insulin syringes are cheap, ubiquitous, and carry fine volume markings.

The catch is that insulin syringes are calibrated to insulin, which has a fixed concentration of 100 units per milliliter (the "U-100" standard). "20 units" on a U-100 syringe is always exactly 0.20 mL of liquid, regardless of what's in the syringe. Semaglutide doesn't have a fixed concentration, so "units" on the syringe correspond to different milligrams depending on the vial.

The math, once and for all

Two formulas are all you need:

Volume (mL) = Dose (mg) ÷ Concentration (mg/mL)
Units (U-100) = Volume (mL) × 100

Put them together:

Units = (Dose ÷ Concentration) × 100

Example: your dose is 0.25 mg, your vial is 5 mg/mL.

1. 0.25 ÷ 5 = 0.05 mL
2. 0.05 × 100 = 5 units

Draw to the "5" mark on a U-100 syringe. Done.

Quick-reference table

Most compounded semaglutide vials come in one of three standard strengths. Here are the units for all common weekly doses:

Dose	2.5 mg/mL vial	5 mg/mL vial	10 mg/mL vial
0.25 mg	10 units	5 units	2.5 units
0.5 mg	20 units	10 units	5 units
1.0 mg	40 units	20 units	10 units
1.7 mg	68 units	34 units	17 units
2.4 mg	96 units	48 units	24 units

Two observations. First, the 2.5 mg/mL vial forces some doses close to (or over) the 100-unit capacity of a standard 1 mL U-100 syringe, which is why many pharmacies default to 5 or 10 mg/mL for patients titrating past 2 mg. Second, the 10 mg/mL vial gives you volumes so small (a quarter-unit here and there) that precision becomes finicky. If your vial and dose don't land cleanly on a unit mark, call your pharmacist — the most common fix is simply a vial at a different strength.

5 common pitfalls

1. Assuming all vials are the same concentration

This is the single biggest mistake we see. If you refill and your new vial is 2.5 mg/mL instead of 5 mg/mL, your unit count doubles. Always re-read the concentration when you pick up a refill — it is printed on the vial, usually in small type next to the total mg.

2. Confusing mg with mcg

A handful of compounded pharmacies label vials in micrograms (mcg) rather than milligrams. 5 mg/mL is the same as 5,000 mcg/mL. If your prescription is written in mg and your vial is in mcg, the units math is different. When in doubt, call the pharmacy.

3. Drawing air and calling it medication

Dose "units" only matter if there's liquid in the syringe. Always check for air bubbles after drawing. Hold the syringe needle-up, tap the barrel to float bubbles to the top, and push the plunger just enough to expel them. Then verify the unit reading one more time.

4. Reading the wrong side of the plunger

Dose volume is read from the flat top of the plunger's rubber stopper, not the tip. In most U-100 syringes this is obvious, but the design varies. When in doubt, practice with saline or a sterile vial before your first semaglutide draw.

5. Using a non-U-100 syringe

U-500 insulin syringes exist (for concentrated insulin). They have the same overall markings but each "unit" equals 5× the volume. Never use a U-500 syringe for semaglutide. Always confirm your syringe says U-100 on the barrel.

Picking a syringe

Insulin syringes come in three common barrel sizes: 0.3 mL (30 units max), 0.5 mL (50 units), and 1 mL (100 units). For a typical semaglutide dose:

• Doses under 30 units: use a 0.3 mL / 30-unit syringe. The markings are wider and easier to read for small doses.
• Doses 30–50 units: a 0.5 mL syringe is the sweet spot.
• Doses over 50 units: use a 1 mL / 100-unit syringe.

Needle length matters less than you would think for subcutaneous injection. Most pharmacies dispense 5/16-inch (8 mm) or 3/16-inch (5 mm) needles in 29–31 gauge. Shorter and thinner is usually more comfortable. Semaglutide is injected subcutaneously — pinch a fold of fat (abdomen, thigh, or upper arm), insert the needle perpendicular, inject, hold for a few seconds, and remove. Rotate sites weekly to prevent injection-site reactions.

FAQ

My vial is 5 mg in 2 mL. What's my concentration?

5 mg ÷ 2 mL = 2.5 mg/mL. Use that figure in the formula.

Can I use a tuberculin syringe instead?

You can. Tuberculin syringes are also 1 mL and marked in 0.01 mL increments, which happens to equal 1 unit each on a U-100 scale. Many patients find insulin syringes easier to read because the markings are labeled in units.

Is an "insulin pen needle" the same as an insulin syringe?

No. Pen needles attach to insulin pens and have no barrel. You cannot use a pen needle to draw from a vial.

What if my vial looks cloudy or discolored?

Don't inject. Semaglutide should be clear and colorless. Cloudiness, particulate matter, or unusual color are reasons to call the pharmacy and exchange the vial.

Sources

1. U.S. Food & Drug Administration. Wegovy (semaglutide) prescribing information. Novo Nordisk. Reviewed April 2026.
2. U.S. Food & Drug Administration. Ozempic (semaglutide) prescribing information. Novo Nordisk. Reviewed April 2026.
3. Becton Dickinson. "Understanding insulin syringes: U-100 and U-500." Patient education leaflet.
4. United States Pharmacopeia. USP <797> and USP <795> standards for compounded sterile preparations.

About the author & reviewer

Editorial Team: the internal staff of Semaglutide Dosage. Pharmacist review: Audrey P. Baysa, RPh, MSc, registered pharmacist with a focus on metabolic medications.