Insulin Dilution Calculator
Medically reviewed by Dr. Chhaya Makhija, MD, DipABLM — September 2026
Work out how much insulin and diluent to combine to reach a target concentration — such as U-10 or U-50 made from standard U-100 — for accurate small or pediatric doses.
Standard insulin is U-100 (100 units/mL).
Standard U-100 insulin delivers one unit in one hundredth of a millilitre. For an adult that precision is ample. For a 4 kg infant or a 3 kg cat needing half a unit, it is not remotely enough — the volume involved sits below what any syringe can measure reliably, and the difference between 0.5 and 0.75 units becomes a matter of eyeballing a gap between two lines.
Dilution solves this by trading concentration for measurable volume. Diluting U-100 to U-10 makes one unit occupy a tenth of a millilitre instead of a hundredth — ten times the volume for the same dose, and a syringe mark you can actually read.
Two cautions matter more than the arithmetic. First, only some insulins can be diluted, and only with the manufacturer's own diluent; using saline or water degrades the insulin unpredictably, and the long-acting analogs generally cannot be diluted at all. Second, a diluted vial is a labelling hazard — a syringe drawn to "5" now contains a different dose than the same mark on undiluted insulin.
The calculator below works out the volumes. Beneath it you will find common dilutions, which products are suitable, and the labelling and storage requirements.
How to Use This Calculator
- Enter the stock concentration — usually 100 units/mL (U-100).
- Enter the target concentration you want, such as 10 for U-10 or 50 for U-50.
- Enter the final volume to prepare in millilitres.
- Read the result: how much insulin to draw up and how much diluent to add.
This is an educational volume estimate. Diluted insulin must be prepared with the manufacturer's diluent under a pharmacist's direction, then labelled with the concentration and date.
How Insulin Dilution Works
Diluting insulin lets very small doses be measured accurately — common in neonatal, pediatric, and small-pet care where a fraction of a unit matters. You mix a measured amount of concentrated insulin with sterile diluent so each mL contains fewer units. The volumes follow a simple dilution relationship:
Example: to make 10 mL of U-10 from U-100 insulin → 10 × (10 ÷ 100) = 1 mL insulin + 9 mL diluent.
Common Dilutions from U-100
| Target | Dilution | Per 10 mL prepared |
|---|---|---|
| U-50 | 1:2 | 5 mL insulin + 5 mL diluent |
| U-25 | 1:4 | 2.5 mL insulin + 7.5 mL diluent |
| U-10 | 1:10 | 1 mL insulin + 9 mL diluent |
| U-1 | 1:100 | 0.1 mL insulin + 9.9 mL diluent |
Diluted insulin is typically stable for a limited time (often ~4 weeks refrigerated) — always follow the manufacturer's guidance and label with the date.
Which Insulins Can Be Diluted (and Which Can't)
Usually dilutable — with the right diluent
Rapid-acting analogues such as lispro (Humalog) and aspart (NovoLog), plus regular and NPH insulin, can be diluted using the sterile diluent made by that insulin's manufacturer. This is the common approach for very small pediatric and neonatal doses.
Should not be diluted
The long-acting analogues glargine (Lantus / Toujeo), detemir (Levemir) and degludec (Tresiba) are generally not diluted. Glargine in particular depends on its acidic pH to work as a basal insulin, so diluting it changes how it is absorbed. For smaller basal doses, the care team adjusts the regimen rather than diluting.
Never substitute tap water for diluent. If the manufacturer's diluent is unavailable, only a pharmacist should decide on any alternative.
Frequently Asked Questions
How do you dilute U-100 insulin to U-10?
Mix 1 part U-100 insulin with 9 parts diluent. For 10 mL of U-10, that is 1 mL insulin plus 9 mL of the manufacturer's diluent. Always use the sterile diluent made for that specific insulin.
What can I use to dilute insulin?
Only the specific sterile diluent supplied by the insulin's manufacturer (for example, the diluent for that brand of rapid-acting insulin). Do not use water, saline, or another insulin's diluent unless a pharmacist directs it — the wrong fluid can change potency and stability.
Why dilute insulin at all?
Dilution makes tiny doses measurable. In infants, young children, and very small pets, a dose may be a fraction of a unit — too small to draw accurately at U-100, so a diluted concentration lets each mark on the syringe represent fewer units.
How long does diluted insulin last?
It varies by product, but diluted insulin is often stable for around four weeks refrigerated. Label the vial with the concentration and preparation date, and follow the manufacturer's and pharmacist's stated expiry.
Can you dilute long-acting insulin like glargine (Lantus)?
Generally no. Glargine, detemir and degludec are not meant to be diluted — glargine relies on its acidic pH to release slowly, so diluting it changes how it works. For smaller basal needs, the care team adjusts the dose or regimen instead of diluting.
How do you measure a very small insulin dose accurately?
Two main ways: use a small-capacity syringe with fine markings (a 0.3 mL U-100 syringe, often with half-unit marks), or have the insulin diluted so each syringe mark represents fewer units. For doses below about one unit — common in infants and tiny pets — dilution is often the more reliable option, set up with a pharmacist.
Sources
- American Diabetes Association. Standards of Care in Diabetes. Insulin administration and pediatric dosing. Link
- Manufacturer prescribing information for rapid- and short-acting insulins (dilution and diluent instructions).
Written by Ryan Mitchell · Last updated: September 2026