Alligation (Mixing Strengths to a Target)
Alligation: how much of two strengths to mix to reach a target strength, or the strength of several lots mixed together.
Open the tool → Runs in your browser. Data leaves only if you deliberately send a problem report from the interactive tool.
Example
- What to work out
- Two strengths to a target
- Strength unit, the same for every strength
- %
- Quantity unit
- g
- Two strengths: the higher strength
- 70
- Two strengths: the lower strength
- 20
- Two strengths: the target strength
- 30
- Two strengths: total wanted
- 500
Result: 100 g of the 70% strength with 400 g of the 20% strength makes 500 g at 30%.
The tool opens with these values already filled in. Replace them with your own.
What you enter
- What to work out: two strengths to a target, or several lots mixed together (medial)
- Strength unit, the same for every strength
- Quantity unit
- Two strengths: the higher strength (100% for pure drug)
- Two strengths: the lower strength (0 for a plain diluent)
- Two strengths: the target strength
- Two strengths: total wanted (give exactly one of this and the two amounts on hand)
- Two strengths: amount of the higher strength on hand
The other 2 fields
- Two strengths: amount of the lower strength on hand
- Several lots: one per line, strength then quantity, separated by a comma
How this is calculated
Citation
Arithmetic identity (mass balance): the drug in the parts equals the drug in the mixture. Parts of the higher strength = target − lower; parts of the lower = higher − target. No source beyond the definition is needed.
A reference and educational tool. Not medical, legal, or financial advice, and not a substitute for clinician judgment.