Syringe calculator

How to use the syringe calculator

1. Dose. Type the dose from your instructions and choose mg or mcg.
2. Strength. Copy the strength from the label. “10 mg/mL” is 10 mg in 1 mL. A label like “20 mg/2 mL” goes in as 20 mg in 2 mL.
3. Syringe. Leave it on Auto to see the smallest U-100 syringe that holds the volume, or pick the size you have.

The answer appears in units and in mL. Below it, the drawing shows where the plunger tip should sit, and the notes warn you if the result falls between printed lines or does not fit the syringe.

The math behind it

A U-100 insulin syringe is scaled at 100 units per mL, so each unit is 0.01 mL.^[1] The calculator does two divisions and one multiplication:

strength (mg/mL) = amount (mg) ÷ volume (mL)
volume (mL) = dose (mg) ÷ strength (mg/mL)
units = volume (mL) × 100

Worked example. The label says 10 mg/mL and the dose is 2.5 mg. 2.5 ÷ 10 = 0.25 mL. 0.25 × 100 = 25 units. On a 0.3 mL syringe that is the line five units below the 30 mark.

Reading the result on a real syringe

The syringe maker's instructions are to pull the plunger slowly until the thin black line at the top of the plunger tip lines up with the mark for your number of units.^[2] In the drawing the needle points left, so that line is the left edge of the dark plunger tip. Each part is named below.

Practise on random syringes in the syringe reading guide.

Pick the syringe that fits

The three sizes and their capacities are standard.^[3] The spacing of the lines is not: 1 mL syringes are made with either 1-unit or 2-unit marks, and ½-unit marks are available on 0.3 mL barrels.^[4] Check what one line means on your own syringe before you measure. On a syringe marked every 2 units, an odd number such as 25 falls between two lines. Details in insulin syringe sizes.

Units are not milligrams

For U-100 insulin, one unit line holds one unit of insulin. For any other liquid, the lines are only volume marks. Twenty units of a 1 mg/mL liquid hold 0.2 mg; twenty units of a 20 mg/mL liquid hold 4 mg. That is why the calculator always asks for the strength.

The scale matters too. Most insulin syringes are U-100.^[1] U-40 insulin for pets is labelled for use with U-40 syringes only, which have 40 units per mL.^[5] U-500 insulin is five times stronger than U-100 and was given with its own U-500 syringe.^[6] This calculator uses the U-100 scale only.

Write doses with care: “mL” rather than “cc”, “units” spelled out rather than “U”, and “mcg” rather than “µg”. All three shortcuts are on the error-prone list of the Institute for Safe Medication Practices.^[7]

Syringe calculators

• mg to unitsCalculator and dose-by-strength chart
• Units to mgWhat a syringe reading contains
• mg to mLVolume for any dose and strength
• mcg to unitsDoses written in micrograms
• How many units in a mL?U-100, U-40 and U-500 answer
• cc to mL1 cc = 1 mL = 100 units
• Concentration calculatormg/mL, mcg/mL, g/L and % w/v
• Units to mLAnd mL to units on U-100, U-40, U-500
• U40 to U100 conversionChart and mix-up checker
• Dilution calculatorC1V1 = C2V2, solve any one value
• mg to mcg1 mg = 1,000 mcg, plus g and ng
• IU to mgFDA factors for vitamins A, D, E

Charts for single doses

Each chart lists one dose at every common strength, with the smallest syringe that holds it and how much a one-unit misreading changes it: 0.25 mg to units, 0.5 mg to units, 1 mg to units, 2.5 mg to units and 5 mg to units.

Syringe guides

• Insulin syringeWhat it is and how it is marked
• Insulin syringe sizesCapacities, markings and needles
• 100 unit insulin syringeThe 1 mL barrel, line by line
• Syringe sizes chartFrom 0.3 mL insulin to 60 mL
• 1 mL syringemL scale vs U-100 units
• 3, 5 and 10 mL syringesGeneral syringes in mL
• How to read an insulin syringeStep by step, with a practice tool
• Tuberculin syringe vs insulin syringeUnits against mL markings
• U40 syringePet insulin and mismatched syringes
• U500 insulin syringe5-unit lines and five-fold errors
• Measuring mistakesThe errors safety groups report
• Sharps disposalSharps containers, the FDA way
• Parts of a syringeBarrel, plunger, tip, needle
• Needle gauge sizesGauge, diameter and length chart