How do I convert a U-40 insulin amount to a U-100 syringe?
Multiply U-40 units by 2.5 to get the U-100 syringe mark for the same volume: 4 U-40 units = 0.1 mL = the 10-unit line on a U-100 syringe. Switching syringe types should be checked with your vet first; this page shows only the math.
The math
volume (mL) = U-40 units ÷ 40 U-100 mark = volume (mL) × 100 Combined: U-100 mark = U-40 units × 2.5 Example: 6 U-40 units ÷ 40 = 0.15 mL → 15 on a U-100 syringe
| U-40 insulin units | Volume (mL) | U-100 syringe mark |
|---|---|---|
| 1 | 0.025 | 2.5 |
| 2 | 0.05 | 5 |
| 3 | 0.075 | 7.5 |
| 4 | 0.1 | 10 |
| 5 | 0.125 | 12.5 |
| 6 | 0.15 | 15 |
| 8 | 0.2 | 20 |
| 10 | 0.25 | 25 |
| 12 | 0.3 | 30 |
| 16 | 0.4 | 40 |
| 20 | 0.5 | 50 |
Confirm with your vet before switching syringes
Switching syringe types should be checked with your vet. Converting marks adds a step where a misread line multiplies into a large volume error, and half-unit amounts become awkward on U-100 lines (1.5 U-40 units is the 3.75 mark, which falls between lines on most U-100 barrels). Your vet can confirm the conversion and whether a matching U-40 syringe is the better option.
Worked examples
2 U-40 units: 2 ÷ 40 = 0.05 mL. On a U-100 syringe that is the 5 mark.
7 U-40 units: 7 × 2.5 = 17.5. On a 0.3 mL U-100 syringe with ½-unit lines that is one half-line past 17; on a 1 mL U-100 syringe with 2-unit lines it falls between lines and cannot be read accurately.
Going the other way: a U-100 mark of 20 holds 0.2 mL, which is 20 ÷ 2.5 = 8 U-40 units.
Check the result fits the barrel
The U-100 mark is always 2.5× the U-40 number, so it fills a small barrel quickly. A 0.3 mL U-100 syringe holds 30 marks, or 12 U-40 units' worth; a 0.5 mL holds 50 marks, or 20 U-40 units' worth. The calculator below converts any number of U-40 units to mL and the matching U-100 mark.
Confirm with your veterinarian: These pages convert syringe marks and volumes only; the number of units your pet gets, and the syringe type to use, come from your vet.
Math only, not medical advice. This page converts numbers; it does not recommend any compound or amount.
Insulin units → mL and syringe mark (premixed insulin, no mixing step)
Enter the number of units to see the volume and where to draw on your syringe.
Math only, not medical advice. Confirm with your veterinarian.