What is the formula for units from mg?

You can combine the last 2 steps by dividing your dose in mg by the vial strength in mg per mL, then multiplying that answer by 100. That gives your units on a standard U-100 syringe.

Does the formula work for U-40 syringes?

A U-40 pet insulin syringe holds 40 units in 1 mL instead of 100, so you would multiply the mL volume by 40 in the final step. Using the wrong multiplier gives the wrong dose, so read the number printed on your syringe barrel, U-40 or U-100, and use that one.

Is this the same formula pharmacists use?

Yes, it is standard ratio arithmetic that divides the dose you need by the concentration you have on hand. Pharmacists use the same math whenever they convert milligram doses into milliliters and syringe units.

Dosage calculator formula

Learn how 3 steps turn the milligrams in your vial, the water volume and your prescribed dose into units for a U-100 insulin syringe.

Use this only as a reference. Your dose is set by your prescriber or by the product label; we only convert it to units.

amount held in 1 unit of a U-100 syringe: 0.01 mL
amount in 100 units: 1 mL
amount in 1 mg: 1,000 mcg in all

The dosage calculator formula turns a dose from your prescriber into the insulin syringe units you need to draw. From your supplies, you need only 3 numbers: how many milligrams the dry vial holds, the mL of water you added and your target dose. After you have those numbers, we calculate your syringe units in 3 brief steps.

The dosage calculator formula in 3 steps

Divide the milligrams in the vial by the mL of water you add to get mg per mL: strength = vial mg / added water mL.
Divide your prescribed dose in mg by the liquid strength to find the injection volume in mL: volume = dose mg / strength.
A U-100 syringe holds 100 units for each 1 mL, so multiply the injection volume by 100 to get syringe units: units = (volume mL) x 100.

An example worked out in plain numbers

Add 2 mL of bacteriostatic water to a 10 mg vial. When you divide 10 mg by 2 mL, the liquid strength is 5 mg per 1 mL.

With a prescribed dose of 0.5 mg, take 0.5 mg and divide it by the 5 mg per mL strength; the liquid volume is 0.1 mL. Multiply 0.1 mL by 100, and the result is 10 units for a U-100 syringe. That result can be checked in our units to mL converter or through the main peptide calculator.

Microgram doses

The vial label prints milligrams, but some prescriptions list the dose in micrograms, written as mcg. Before using the steps, divide the microgram dose by 1,000, because 1 mg equals 1,000 mcg. You can try our mg to mcg converter instead. A 250 mcg dose becomes 0.25 mg after dividing by 1,000. At 5 mg per mL, that amount is 0.05 mL, or 5 units in all.

Verify your result

Before drawing a dose, confirm that your final unit count fits inside the barrel. A 0.3 mL syringe holds up to 30 units only. The peptide syringe calculator lets you compare barrel capacities; water added lowers the strength, which means the same dose needs more units.

Questions people often ask

What's the mg to units formula?

The last 2 steps can be joined: divide the dose in mg by the vial's strength in mg per mL, then multiply the result by 100. The result is the unit count for a standard U-100 syringe.

Will this formula work with U-40 syringes?

A pet insulin syringe marked U-40 holds 40 units in 1 mL, not 100. For that syringe, the final step multiplies the volume in mL by 40. Choosing the wrong multiplier gives you the wrong dose. Check the marking on your barrel, U-40 or U-100, and follow that one.

Do pharmacists use the same formula?

Yes, this is standard ratio arithmetic. It divides the needed dose by the concentration in your supply. Whenever pharmacists change a milligram dose into milliliters and units for a syringe, they use the same math.