How do you read a 100-unit (U-100) syringe?
A 100-unit syringe is a U-100, 1 mL syringe: 100 unit marks fill 1 mL, so every unit is 0.01 mL. To convert, divide units by 100 to get mL, or multiply mL by 100 to get units. 10 units = 0.1 mL, 25 units = 0.25 mL, 50 units = 0.5 mL.
The math
1 unit (U-100) = 1 mL ÷ 100 = 0.01 mL mL = units ÷ 100 units = mL × 100 Example: 35 units ÷ 100 = 0.35 mL
| U-100 units | mL | Fits 0.3 mL barrel? | Fits 0.5 mL barrel? |
|---|---|---|---|
| 1 | 0.01 | yes | yes |
| 5 | 0.05 | yes | yes |
| 10 | 0.1 | yes | yes |
| 20 | 0.2 | yes | yes |
| 25 | 0.25 | yes | yes |
| 30 | 0.3 | yes | yes |
| 40 | 0.4 | no | yes |
| 50 | 0.5 | no | yes |
| 75 | 0.75 | no | no |
| 100 | 1 | no | no |
Reading the marks
On a full 1 mL (100-unit) barrel the numbers usually run 10, 20, 30 … 100, with a short line every 2 units. That means each small line is 0.02 mL, and an odd number like 15 units sits halfway between two lines. Read from the top edge of the plunger seal (the flat ring nearest the needle), not the domed tip.
Smaller U-100 barrels use the same unit size but finer spacing: a 0.5 mL (50-unit) and a 0.3 mL (30-unit) syringe usually mark every single unit, and some 0.3 mL barrels add half-unit lines. If your number is under about 30 units, the smaller barrel is easier to read accurately.
Worked examples
22 units on a 100-unit syringe: 22 ÷ 100 = 0.22 mL. On a 1 mL barrel that is one small line past 20.
0.45 mL to units: 0.45 × 100 = 45 units, on a 1 mL barrel with 2-unit lines that is halfway between the 44 and 46 lines; a 0.5 mL barrel marks 45 directly.
From an amount instead of a volume: 5 mg in 2 mL is 2.5 mg/mL. 250 mcg (0.25 mg) ÷ 2.5 = 0.1 mL = 10 units on the 100-unit syringe. The calculator below does this step for any vial and water volume.
Not every syringe is U-100
"Units" only mean 0.01 mL on a U-100 barrel. A U-50 unit is 0.02 mL and a U-40 unit is 0.025 mL, so the same number of units is a different volume. Check the label on the package or barrel before converting.
Math only, not medical advice. This page converts numbers; it does not recommend any compound or amount.
Concentration = 5 mg ÷ 2 mL = 2.5 mg/mL Volume = 250 mcg ÷ 2500 mcg/mL = 0.1 mL Units = 0.1 mL × 100 (U-100) = 10 units
U-100 syringe · 100-unit barrel. Illustration only; read the marks on your actual syringe.
Math only, not medical advice. Verify every number yourself.
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