Calculator 101, dose math one card at a time

Card 1 of 8

Two vials, two draws

Two syringes from two 5 mg vials. A, mixed with 2 mL of water, is drawn to 10 units. B, mixed with 3 mL of water, is drawn to 15 units.

Which draw holds more peptide?

• A
• B
• Same. Both draws hold 2 dots, 250 mcg each.

Same, 250 mcg each.

B's extra water spread the peptide, so the same dose takes more liquid.

Your dose is peptide. Your draw is liquid.

Card 2 of 8

A unit is liquid

A 1 mL syringe. A bracket from 0 units to 100 units is labeled 1 mL.

How much liquid is 10 units?

• 10 mL
• 1 mL
• 0.1 mL. 100 units = 1 mL, so 10 units = 0.1 mL.

0.1 mL. Syringe units measure liquid, never peptide. Even when a vial is labeled in IU, 1 unit on the syringe is 0.01 mL.

Check that the syringe says U‑100. On a U‑40 syringe, 10 units is 0.25 mL.

100 units = 1 mL.

Card 3 of 8

What the label counts

A 5 mg vial of dry powder, drawn as 40 dots, with 2 mL of water about to go in.

Add 2 mL of water. How much peptide is in the vial?

• 5 mg in each mL, 10 mg in all
• 5 mg in all. The water spread the same 5 mg through 2 mL.
• Less than 5 mg

Still 5 mg, spread through the water like a drink mix.

At 1,000 mcg per mg, that's 5,000 mcg.

Water spreads the peptide. It never changes how much.

Card 4 of 8

Each unit holds

5,000 mcg spread through 2 mL of water, drawn as a bar of 200 units.

5,000 mcg in 2 mL of water, which is 200 units. What does each unit hold?

• 25 mcg. 5,000 mcg ÷ 200 units = 25 mcg in each unit.
• 2.5 mcg
• 40 mcg

5,000 mcg ÷ 200 units = 25 mcg in each unit.

The calculator's "Show the math" lists this as 2,500 mcg/mL. That's the same mix, counted per mL.

What each unit holds = mcg in the vial ÷ units of water.

Card 5 of 8

Your draw

A 5 mg vial in 2 mL of water. The syringe fills to 10 units, 0.1 mL, and the counter reaches 250 mcg, one dot every 5 units.

Why 10 units?

• 10 units always hold 250 mcg
• Each unit holds 25 mcg. 10 units × 25 mcg = 250 mcg, so the draw follows what each unit holds.
• Because the vial is 5 mg

250 mcg ÷ 25 mcg = 10 units.

Check it. 10 units × 25 mcg = 250 mcg.

10 mg vial in 2 mL. Each unit holds 50 mcg. Your dose is 300 mcg. Set the plunger. 300 mcg ÷ 50 mcg = 6 units. 6 units × 50 mcg = 300 mcg.

10 mg vial in 2.5 mL. Your dose is 0.6 mg. What does each unit hold?

• 40 mcg. 10,000 mcg ÷ 250 units = 40 mcg in each unit.
• 4 mcg
• 25 mcg

Each unit holds 40 mcg. Set the plunger for 0.6 mg. 600 mcg ÷ 40 mcg = 15 units. 0.6 mg = 600 mcg, and 15 units × 40 mcg = 600 mcg.

Draw = dose in mcg ÷ what each unit holds.

Card 6 of 8

More water, same dose

You add more water. Your dose stays 250 mcg. What happens to your draw?

• Goes up. Each unit now holds less, so 250 mcg takes more units.
• Goes down
• Stays the same

It goes up. Each unit holds less, so 250 mcg takes more units.

Double the water and the draw doubles. The dose stays 250 mcg.

• 1 mL of water. Each unit holds 50 mcg. Draw 5 units, between the lines for 4 units and 6 units. 20 doses in the vial.
• 1.5 mL of water. Each unit holds about 33.3 mcg. Draw 7.5 units, between the lines for 6 units and 8 units. 20 doses in the vial.
• 2 mL of water. Each unit holds 25 mcg. Draw 10 units. 20 doses in the vial.
• 2.5 mL of water. Each unit holds 20 mcg. Draw 12.5 units, between the lines for 12 units and 14 units. 20 doses in the vial.
• 3 mL of water. Each unit holds about 16.7 mcg. Draw 15 units, between the lines for 14 units and 16 units. 20 doses in the vial.

Your friend mixed a 5 mg vial with 3 mL of water and draws 15 units for 250 mcg.

• 1 mL water. 15 units hold 750 mcg, 3 times your 250 mcg dose.
• 1.5 mL water. 15 units hold 500 mcg, 2 times your 250 mcg dose.
• 2 mL water. 15 units hold 375 mcg, 1.5 times your 250 mcg dose.
• 2.5 mL water. 15 units hold 300 mcg, 1.2 times your 250 mcg dose.
• 3 mL water. 15 units hold 250 mcg, your dose.

Copy the dose, never the draw.

Water moves the draw, never the dose.

Card 7 of 8

Find your units

A close view of a 1 mL syringe from 0 units to 20 units, numbered at 10 units and 20 units, with 5 spaces between the zero line and 10 units.

How many units is each line on this barrel worth?

• 1 unit
• 2 units. Five spaces split 10 units into 2 units each.
• 5 units

2 units. Five spaces take you from 0 units to 10 units.

Tap 6 units. 6 units sits on the third line past 0 units.

5 units sits halfway between the lines for 4 units and 6 units.

Read your draw at the flat front edge of the rubber plunger, the edge nearest the needle. Barrels differ. Some 1 mL barrels have a line for every unit, and so does a 0.5 mL barrel. A 0.3 mL barrel has one for every unit or every half unit. Count the spaces on yours.

Read the numbers, then count the spaces.

Card 8 of 8

Check your number

A 5 mg vial in 2 mL of water. A calculator says 100 units for a 250 mcg dose.

A calculator says 100 units for your 250 mcg dose. What do 100 units hold?

• 250 mcg
• 2,500 mcg. 100 units × 25 mcg = 2,500 mcg, ten times your dose. The right draw is 10 units.
• 100 mcg

100 units × 25 mcg = 2,500 mcg, ten times your 250 mcg dose. The right draw is 10 units.

A big draw can be right too, so multiply back instead of judging by size.

Count the vial

Your dose is 250 mcg, twice a week. How long does this vial last?

• 10 weeks. At twice a week, 20 doses last 10 weeks.
• 20 weeks
• 20 days

5,000 mcg ÷ 250 mcg = 20 doses.

At twice a week, 20 doses last 10 weeks. Once a day, they last 20 days.

Ending one dose short is normal. If you end two or more doses short, or have a dose left over, redo the math.

Multiply back on every new vial. Doses in the vial = mcg in the vial ÷ dose in mcg, rounded down.