How do I use Belle's dosage calculator?

Belle has a dosage calculator on the website. It converts between the weekly dose your provider prescribed, written in milligrams, and the number of units you draw into the syringe.

What it asks you for

It works in either direction. You can start from your dose in milligrams and get units, or start from units and get milligrams. Then it asks for four things:

• Which medication you take, tirzepatide or semaglutide.
• Which pharmacy filled your vial.
• The concentration printed on your vial label.
• Your prescribed weekly dose.

If your pharmacy is not one of the options, or the concentration on your label is not one of the options, choose "Other" and type the number from your label.

What it gives you

It shows the number of units to draw, the matching volume in milliliters, and a picture of a syringe with the mark to draw to.

Doing the math yourself

You can double check the calculator with three rules. They work on a standard 100-unit syringe, where 100 units is 1 mL and 1 unit is 0.01 mL.

• Units to milligrams: units × concentration (mg/mL) ÷ 100 = mg
• Milligrams to units: mg ÷ concentration (mg/mL) × 100 = units
• Milliliters to milligrams: mL × concentration (mg/mL) = mg

Here is what that looks like for two common concentrations:

Other examples:

• At 2.5 mg/mL, 20 units is 0.5 mg.
• 5 mg from an 18 mg/mL vial is 5 ÷ 18 × 100 = about 27.8 units.
• The same milligram dose is a different number of units at different concentrations. For example, 1 mg is 40 units at 2.5 mg/mL and 25 units at 4 mg/mL.
• A prescription written in mL works the same way: 0.37 mL is 37 units. At 20 mg/mL that is about 7.4 mg, which is what your care team calls a 7.5 mg dose (the exact 7.5 mg is 37.5 units).

If your math lands between two marks on the syringe, ask your care team which whole number to draw. They give you the exact amount for your vial. More than 100 units will not fit in one standard syringe; see "Your syringe and your dose" below.

Why it needs your vial label

Units are not a dose. The same weekly dose comes out as a different number of units in two different vials, because units depend on how concentrated the liquid is. That is why the calculator cannot tell you anything until you give it the number from your label, and it is why a unit count on its own never tells you what your dose is. There is more on this in "Dose vs. concentration: why your vial says a bigger number".

Reading the concentration on your label

The calculator needs the concentration in mg per mL. Some labels show it that way (for example, 20 mg/mL). Others show the total milligrams in the vial and the total volume (for example, 15 mg/0.5 mL). If your label shows total milligrams and volume, divide the milligrams by the milliliters to get mg/mL:

• 15 mg/0.5 mL is 15 ÷ 0.5 = 30 mg/mL.
• 20 mg/3 mL is about 6.7 mg/mL. It is not 20 mg/mL.

Typing 20 when your label says 20 mg/3 mL will give you the wrong number of units. If you are not sure, send a photo of your label to your care team.

Your syringe and your dose

Units mean the same thing on any insulin syringe. If your provider says 25 units, draw to the 25 mark whether your syringe holds 30, 50, or 100 units. Each mark is one unit. A smaller syringe has fewer marks, so your dose has to fit on it. A 30-unit syringe cannot measure a 50-unit dose, for example.

If your syringe is marked in mL instead of units, 0.01 mL is 1 unit.

Check that your dose fits before you draw. A standard syringe holds 100 units (1 mL). If your milligram dose works out to more than 100 units at your vial's concentration, it will not fit in one syringe. For example, 12.5 mg from a 10 mg/mL vial works out to 125 units. Do not split it on your own. Message your care team. Depending on your situation, they may tell you to draw it in two parts, or change what is sent at your next refill so that it fits in one injection.

Using the calculator for a different dose

Taking less than your prescribed dose: you can use the calculator to find the units. Enter the smaller dose in milligrams and the concentration (mg/mL) printed on the vial you are using now. This also works for drawing a smaller dose from a stronger vial. Let your care team know you have lowered your dose so your plan and records match.

Taking more than your prescribed dose: message your care team first. Your provider has to approve any dose above your prescription, so do not use the calculator to go higher on your own. See "How to request a dose change."

Your provider's written instructions are the source of truth

The calculator is a way to check your own math. It is not a prescription, and it does not change anything about your plan. The dose and the draw amount that count are the ones your provider wrote on your prescription, and the details printed on your vial label.

If what the calculator shows does not match your written instructions, do not adjust your injection. Message the care team and we will confirm the right draw with your provider.

The calculator is for information only and is not a substitute for medical advice.