Toxin Dilution Calculator
Reconstitution, concentration and dose volumes for UK-licensed aesthetic botulinum toxins.
Enter units to get the volume to inject, or a volume to get the units it delivers.
Each brand's own licensed dose for this area, taken straight from its SPC. These are not a conversion factor to apply to other doses.
Data compiled from the current UK Summary of Product Characteristics (emc / medicines.org.uk) for each product. Licensed doses shown are the SPC regimens; off-licence use is a clinical and prescribing decision. This tool does not replace the SPC or clinical training.
This free botulinum toxin dilution calculator helps UK clinicians reconstitute aesthetic toxins accurately — working out the concentration you get from a given volume of saline, the saline needed to hit a target concentration, and the exact injection volume for each licensed dose. It covers seven UK-licensed aesthetic toxins, with dosing data taken from each product's current Summary of Product Characteristics (SPC).
How to use the toxin dilution calculator
Start by selecting your product. For powder toxins, choose your vial size, then either enter the volume of saline you are adding (forward dilution) to see the resulting concentration, or enter your target concentration (reverse dilution) to see how much saline to add. The tool then shows the concentration in units per 0.1 ml, a units ↔ volume converter, and a table of the licensed doses expressed as injection volumes at your chosen concentration. Ready-to-use liquid toxins skip reconstitution and display their as-supplied concentration directly.
What is botulinum toxin reconstitution?
Most aesthetic toxins are supplied as a freeze-dried powder that must be reconstituted with sterile 0.9% sodium chloride (saline) before use. The volume of saline you add determines the final concentration: less saline gives a more concentrated solution (smaller injection volumes), more saline gives a more dilute solution (larger, more diffuse volumes). Getting this right is fundamental to dosing accurately and predictably, which is why a reliable dilution reference matters.
Forward vs reverse dilution — what's the difference?
Forward dilution answers “if I add this much saline, what concentration do I get?” Reverse dilution answers the more practical clinical question “I want this concentration — how much saline should I add?” This calculator does both, so you can either check a familiar reconstitution or plan a new one against your preferred units-per-0.1 ml.
Why are toxin units never interchangeable between brands?
This is the single most important safety point. The “units” of one botulinum toxin are not equivalent to the units of another. Speywood units (used for abobotulinumtoxinA products such as Azzalure and Alluzience) are not the same as Allergan units (onabotulinumtoxinA) or the units used by other brands. You cannot simply carry a dose across from one product to another. Any cross-brand figure — including the approximate comparison in this tool — is a prescriber's starting reference only, never a licensed conversion. Always dose to the specific product's SPC and to clinical assessment.
Which toxins does this calculator cover?
The tool includes seven botulinum toxins licensed for aesthetic use in the UK, using data compiled from their current SPCs on the electronic medicines compendium (emc):
- Azzalure (abobotulinumtoxinA) — powder, Speywood units
- Bocouture (incobotulinumtoxinA) — powder, units
- Botox (onabotulinumtoxinA) — powder, Allergan units
- Letybo (letibotulinumtoxinA) — powder, units
- Nuceiva (prabotulinumtoxinA) — powder, units
- Alluzience (abobotulinumtoxinA) — ready-to-use liquid, Speywood units
- Relfydess (relabotulinumtoxinA) — ready-to-use liquid, units
Safe practice and compliance
Botulinum toxin is a prescription-only medicine (POM). It must be prescribed by an appropriate prescriber following a suitable consultation, reconstituted and stored per the SPC, and administered by a suitably trained professional working within their scope of practice. Reconstitute only with the diluent and volume the SPC allows, use each vial within its stated post-reconstitution window, and dispose of sharps and unused product appropriately.
Related clinician tools & guides
Frequently asked questions
How do I reconstitute botulinum toxin?
Reconstitute the freeze-dried powder with sterile 0.9% sodium chloride, using the diluent volume specified in the product's SPC. The volume you add sets the concentration — enter it into the calculator's forward mode to confirm your units per 0.1 ml, or use reverse mode to find the saline volume for a target concentration.
What concentration should I dilute to?
There is no single “correct” concentration; it depends on the product, the area and clinician preference within the SPC. Many powder toxins are commonly reconstituted to around 4 units per 0.1 ml, but you should always work within the SPC's stated reconstitution range. Use reverse dilution to calculate the exact saline volume for your chosen concentration.
Can I convert a dose from one toxin brand to another?
Not with a licensed, official factor — units are not interchangeable between brands. The calculator offers an approximate cross-brand comparison as a prescriber's starting reference only. abobotulinumtoxinA (Speywood units) is commonly cited at roughly 2.5:1 versus onabotulinumtoxinA, with reviews reporting a debated 2:1–3:1 range. Always dose to the specific SPC.
Which toxins are ready-to-use and need no reconstitution?
Alluzience and Relfydess are supplied as ready-to-use liquids, so they are not reconstituted. The calculator flags these and shows their as-supplied concentration directly.
Is the toxin dilution calculator free to use?
Yes. It is a free educational tool for registered clinicians, provided by Harley Supplies. No login is required to use it.
Is this tool a substitute for the SPC?
No. It is a calculation aid built from published SPC data to speed up routine reconstitution maths. Always verify doses and reconstitution against the current SPC and your clinical judgement before treating.
References
- electronic medicines compendium (emc). Summaries of Product Characteristics for Azzalure, Bocouture, Botox/Vistabel, Letybo, Nuceiva, Alluzience and Relfydess. medicines.org.uk.
- Medicines and Healthcare products Regulatory Agency (MHRA). Botulinum toxin products: prescribing and supply as prescription-only medicines. gov.uk.
For registered healthcare professionals. Dosing data is compiled from current UK SPCs and provided for educational purposes; SPCs are updated periodically, so verify the current document before use. This tool does not constitute prescribing advice.
Dr Emmaline Ashley
Aesthetic Doctor · GMC 7582958 · COO of Harley Supplies
Dr Emmaline Ashley is an aesthetic doctor and published researcher in aesthetic medicine. This calculator was built from current UK Summaries of Product Characteristics and clinically reviewed for accuracy.
Source UK-licensed toxins from a clinician-founded supplier
Open your Harley Supplies trade account for genuine, traceable stock at trade pricing, with the clinical support to match.
Open your trade account →