Insulin Conversion & Supply Calculators
Convert insulin doses between units, millilitres (mL) and milligrams, match a dose to the right syringe, and plan how long a vial or pen will last. This hub also converts blood glucose between mg/dL and mmol/L and translates A1c into estimated average glucose. Every tool is educational and built on insulin product labeling and the ADA Standards of Care.
🔄 Insulin Unit & Volume Conversion Tools
Move accurately between units, mL and mg across U-40, U-100, U-200, U-300 and U-500 concentrations, and find the matching syringe marking.
Insulin Conversion Calculator
All-in-one converter: units ↔ mL ↔ mg across U-100, U-200 and U-500 in a single step.
Insulin Units to mL
Convert a unit dose to millilitres for U-40, U-100, U-200, U-300 or U-500 insulin.
mL to Insulin Units
Work backwards from a volume in millilitres to the number of insulin units to draw.
Insulin Units to mg
Convert insulin activity units to milligrams by insulin type for reference and labeling checks.
Insulin Syringe Calculator
Find the correct mark on a 0.3, 0.5 or 1 mL U-100 syringe for your prescribed dose.
Insulin Dilution Calculator
Mix insulin with diluent to a lower strength such as U-10 or U-50 for very small doses.
📊 Blood Glucose & A1c Conversion Tools
Convert glucose readings between mg/dL and mmol/L, and translate A1c into estimated average glucose (eAG) and back.
Blood Glucose Unit Converter
Convert any reading between mg/dL (US) and mmol/L (UK, Canada, EU, Australia).
A1c to Average Glucose
Turn an HbA1c percentage into estimated average glucose (eAG) using the ADAG formula.
eAG to A1c
Convert an average glucose value back to an estimated A1c, in mg/dL or mmol/L.
HbA1c Calculator
Estimate A1c from your recent average glucose to gauge longer-term control.
GMI Calculator
Glucose Management Indicator — an A1c-style estimate from your CGM mean glucose.
📦 Supply, Refill & Prescription Planning
Estimate how long your insulin will last, how many vials or pens you need, and when to refill — useful for travel and pharmacy planning.
Insulin Day Supply
How many days a vial or pen lasts at your current daily dose, with the 28-day open rule.
Insulin Vial Calculator
Units per vial, how long each vial lasts, and how many vials a prescription needs.
Insulin Pen Calculator
Doses remaining in a pen, units per click, and how many days one pen covers.
Pens Per Month
Estimate how many pens or boxes you need each month for your prescription refill.
Insulin Refill & Days Supply
Days supply and a refill-by date from your dose and the units dispensed.
How insulin unit and concentration conversion works
Insulin is dosed in units of biological activity, but it is drawn and stored as a liquid volume. The bridge between the two is the concentration printed on the label — the "U-number" — which tells you how many units sit in each millilitre. Once you know the concentration, the conversion is simple arithmetic.
Core conversion formulas
Example: 30 units of U-100 insulin = 30 ÷ 100 = 0.30 mL. The same 0.30 mL of U-500 insulin would hold 0.30 × 500 = 150 units — which is why concentration always has to match the syringe.
Common insulin concentrations
| Strength | Units per mL | 1 unit equals | Typical use |
|---|---|---|---|
| U-40 | 40 units/mL | 0.025 mL | Some veterinary insulins |
| U-100 | 100 units/mL | 0.01 mL | Standard human insulin (most products) |
| U-200 | 200 units/mL | 0.005 mL | Concentrated pens (e.g. lispro U-200, degludec U-200) |
| U-300 | 300 units/mL | 0.0033 mL | Glargine U-300 (Toujeo) |
| U-500 | 500 units/mL | 0.002 mL | Severe insulin resistance (Humulin R U-500) |
Safety first: a U-100 syringe is calibrated for 100 units/mL only. Using it with a different concentration — or drawing U-500 into a U-100 syringe — is a well-known cause of fivefold dosing errors. Concentrated insulins are designed to be given with their own pen or a matching syringe.
Estimating how long your insulin will last
Supply planning answers two everyday questions: how many days will this vial or pen cover? and how many do I need for a 30- or 90-day prescription? Both come from the total units in the container and your average units per day.
Days supply formula
A 10 mL U-100 vial holds 1,000 units; a 3 mL U-100 pen holds 300 units. At 40 units/day, a vial lasts 1,000 ÷ 40 = 25 days. Remember the 28-day rule: most opened vials and pens should be discarded after about 28 days even if insulin remains, so refill planning should use whichever comes first.
Frequently Asked Questions
How do I convert insulin units to milliliters (mL)?
Divide the number of units by the insulin's concentration. For standard U-100 insulin, mL = units ÷ 100, so 1 unit = 0.01 mL and 25 units = 0.25 mL. For U-40 divide by 40, for U-200 by 200, and for U-500 by 500. Always draw the dose with a syringe matched to that concentration.
What is the difference between U-100 and U-500 insulin?
The number is the concentration in units per millilitre. U-100 contains 100 units/mL and is the most common strength. U-500 (Humulin R U-500) is five times more concentrated at 500 units/mL and is reserved for severe insulin resistance. Because the same volume holds five times the dose, U-500 requires a dedicated U-500 syringe or pen — never a standard U-100 syringe.
How many units are in an insulin pen or vial?
A standard 3 mL U-100 insulin pen holds 300 units, and a 10 mL U-100 vial holds 1,000 units. More concentrated insulins hold more units in the same volume — a 3 mL U-200 pen contains 600 units, for example.
How long will one vial of insulin last?
Divide the total units in the container by your average units per day. A 1,000-unit U-100 vial used at 40 units/day lasts about 25 days. Most opened vials and pens should also be discarded after 28 days regardless of remaining insulin, so use the shorter of the two figures for refill planning.
How do I convert blood glucose between mg/dL and mmol/L?
Divide mg/dL by 18 to get mmol/L, and multiply mmol/L by 18 to get mg/dL. For example, 180 mg/dL ÷ 18 = 10 mmol/L. mg/dL is used in the US, while mmol/L is standard in the UK, Canada, Australia and most of Europe.
Can I use a U-100 syringe to draw U-500 insulin?
No. Drawing U-500 insulin into a U-100 syringe causes serious dosing errors because the marks assume 100 units/mL. U-500 must be given with a dedicated U-500 syringe or the U-500 KwikPen, which are calibrated for 500 units/mL. Confirm any concentration change with your prescriber or pharmacist.
Sources
- American Diabetes Association. Standards of Care in Diabetes — 2024. Section 6 (Glycemic Goals) and Section 9 (Pharmacologic Approaches to Glycemic Treatment).
- U.S. FDA prescribing information for Humulin R U-500, Toujeo (insulin glargine U-300), and concentrated U-200 insulin pens.
- Nathan DM et al. "Translating the A1C assay into estimated average glucose values (ADAG study)." Diabetes Care. 2008;31:1473–1478.
Last reviewed: June 2025 · Conversions verified against insulin product labeling and ADA Standards of Care 2024