The parts you read
- Needle. Sized as length × gauge, for example 6 mm × 31G.
- Barrel. Holds the liquid. The scale is printed on it.
- Unit scale. Numbered lines. On this 0.5 mL syringe each line is 1 unit.
- Plunger tip. Line up the thin black line at its top with the mark for the dose. Here it sits on 10.
- Liquid. The measured dose between the 0 mark and the plunger tip: 10 units = 0.1 mL.
- Plunger rod. Pull to draw liquid in, push to inject.
- Flange. Finger grip at the end of the barrel.
- Thumb press. Where the thumb pushes the plunger.
Step 1: find out what one line is worth
Look at two numbered lines and count the small lines between them. Insulin syringes are made with ½-unit, 1-unit or 2-unit lines depending on the size and model.[4] For example, if the numbers go 0, 10, 20 and there are five spaces between 0 and 10, each line is 2 units.
| Barrel | Holds | Made with lines of |
|---|---|---|
| 0.3 mL | 30 units | 1 unit or ½ unit |
| 0.5 mL | 50 units | 1 unit |
| 1 mL | 100 units | 1 unit or 2 units |
Step 2: how to read a syringe plunger
embecta's instructions: pull the plunger down slowly, aligning the thin black line of the plunger with the desired number of units.[1] In these drawings the needle points left, so that line is the left edge of the dark plunger tip, marked with a dashed orange line.
Step 3: count from the nearest number
Start at the last numbered line below the plunger tip and add the lines after it. Three worked examples:
0.3 mL · 1-unit lines · reads 7 units (0.07 mL)
0.5 mL · 1-unit lines · reads 23 units: 20 + 3 lines
1 mL · 2-unit lines · reads 36 units: 30 + 3 lines × 2
Step 4: check for air and look again
Air bubbles take up space that should hold the dose. MedlinePlus advises tapping the syringe so bubbles float to the top, pushing the air back into the vial, and drawing again.[2] If there are many bubbles, redraw and recheck.[3] Then look at the syringe again to make sure you have the right dose.[2]
Hard to see the lines?MedlinePlus notes that magnifiers that clip onto the syringe can make the markings easier to read.[2]
Practise reading
The trainer draws a random 0.3, 0.5 or 1 mL U-100 syringe. Type what you read; it tells you if you are right and how to count it.
Syringe reading trainer
random syringe · read the plunger tip0.5 mL syringe · 50 units · each line = 1 unit
0 of 0 correct
Before you draw up
The order MedlinePlus and embecta describe for drawing from a vial: pull in as much air as the dose, inject that air into the vial, turn the vial upside down with the needle tip in the liquid, then pull the plunger slowly to the dose line.[2][3][1] Follow the instructions your own prescriber, nurse or pharmacist gives you; this page is about reading the scale.
Once you can read the scale, the mg to units calculator tells you which line a dose in mg falls on, and units to mg works backwards from a reading. The sizes and line spacings you may meet are compared in insulin syringe sizes, and the most common reading errors are in syringe measuring mistakes.
Frequently asked questions
Where do you read an insulin syringe?
At the thin black line at the top of the plunger tip, lined up with the mark for your number of units.
How many units is each line on an insulin syringe?
½, 1 or 2 units, depending on the syringe. Count the lines between two numbers to find out.
How to read a syringe in units?
Find what one line is worth, line up the thin black line on the plunger tip with your mark, and count from the nearest number. On a U-100 syringe each unit is 0.01 mL.
How do I read 0.1 mL on an insulin syringe?
On a U-100 syringe 0.1 mL is the 10-unit line.
What does each number on a 1 mL insulin syringe mean?
The numbers are units of U-100 insulin. 10 means 10 units, which is 0.1 mL; 100 means 100 units, which is 1 mL.