Insulin Syringe Unit Conversion Calculator (U-40 vs U-100)
Check whether your insulin concentration and syringe type match before drawing up a dose - a U-40/U-100 mismatch is a common and dangerous source of insulin dosing errors.
Insulin concentration
Vetsulin and ProZinc are U-40. Most human insulins (Humulin N/NPH, Novolin N, Lantus/glargine, Levemir/detemir) are U-100.
Prescribed dose (units)
Syringe type available
How to use this tool
Why concentration matters
U-40 syringes are calibrated for 40 units/mL insulin, and U-100 syringes for 100 units/mL. Vetsulin (porcine lente insulin) and ProZinc (protamine zinc insulin) are U-40 and require U-40 syringes. Most human insulins - Humulin N/NPH, Novolin N, Lantus/glargine, Levemir/detemir - are U-100.
What a mismatch does
Drawing U-40 insulin into a U-100 syringe delivers far LESS insulin than the unit mark implies, risking under-dosing. Drawing U-100 insulin into a U-40 syringe delivers far MORE insulin than the unit mark implies, risking a dangerous overdose and severe hypoglycemia. Up to a 2.5x dosing error is possible.
The safest fix
If the calculator detects a mismatch, the correct action is to obtain the matching syringe type - not to attempt drawing to a converted unit mark on the wrong syringe. Never mix U-40 and U-100 syringes and insulins without triple-checking the math.
Frequently asked questions
Why are there two different insulin syringe types?
U-40 syringes are calibrated for 40 units/mL insulin, and U-100 syringes for 100 units/mL - each syringe's unit markings assume its matching concentration, so the SAME unit mark on each syringe corresponds to a different actual volume and thus a different physical amount of insulin.
What veterinary insulins are U-40?
Vetsulin (porcine lente insulin, used in dogs) and ProZinc (protamine zinc insulin, used in cats and dogs) are both U-40 concentration and require U-40 syringes.
What happens if you draw up U-40 insulin in a U-100 syringe by mistake?
You would draw far LESS actual insulin than intended for the same unit mark, since the U-100 syringe assumes a more concentrated solution than U-40 actually is - this typically results in significant UNDER-dosing, poor glycemic control, and diabetic complications from chronic under-treatment.
What happens if you draw up U-100 insulin in a U-40 syringe by mistake?
The reverse - you would draw far MORE actual insulin than intended for the same unit mark, since the U-40 syringe assumes a less concentrated solution, risking a dangerous OVERDOSE and severe hypoglycemia.