Alligation Calculator

Alligation Pharmacy Calculator_RxCalculations

Created by Michael Danquah, MS, PhD

Last updated: January 29, 2024

Alligation Calculator

Enter the concentrations of both components and the desired concentration. Make sure the units of concentration are the same for both components and the desired concentration. Also, enter the quantity of the component of the the final quantity based on whichever is known.

Use if the quantity of one of the components is given and the final quantity is unknown.

Several occasions arise for pharmacists where there is a need to compound a preparation of a desired concentration using stock preparations. Mixing components of different concentrations in the right proportion to obtain a specified concentration can be tricky.

However, the alligation method is an elegant way to quickly determine the quantities needed in such instances.  But what if there is a calculator that makes this process even faster. The alligation calculator emerges as such an excellent tool for that can be used to make this process extremely efficient and can be an excellent resource when learning the alligation method in pharmaceutical calculations.

This article lays out a step-by-step guide to using the alligation calculator. Read on to see how.

Understanding Alligation

The alligation method is a useful technique in pharmacy to calculate the required concentration of a mixture using two different concentrations. It involves finding the ratio at which solutions of different concentrations must be mixed in order to get the desired intermediate concentration. Watch the video below if you need a quick refresher on the alligation method.

Definition of Alligation

Alligation is a pharmaceutical calculations method that helps mix two components (e.g. solutions) with different concentrations. It figures out how much of each solution you need to end up with a specific concentration.

Pharmacists use this technique to compound preparations that are safe and effective for patients.

By using an alligation calculator, they can quickly find the right quantities of the components. This tool does the math for them, ensuring the final mixture has just what the doctor ordered.

Now let's explore why alligation matters in pharmacy work.

Purpose of Alligation in Pharmacy

Pharmacists often face the task of mixing two components to achieve a specific concentration. This is where alligation comes in handy. It's a method that helps calculate how much of each solution to mix together.

Think about making an ointment with just the right strength, or preparing a pediatric dose that needs to be exact.

Using alligation ensures pharmacists can compound medications safely and accurately. They use it to find the perfect balance between solutions of different strengths.  

Alligation avoids mistakes and saves time in pharmacies every day. It lets pharmacists compound preparations that aren't readily available but are crucial for treatment. The next step is diving into how an alligation calculator simplifies this whole process even further!

How to Use an Alligation Calculator

To use an Alligation Calculator, simply input the values for the two concentrations to be mixed, and the desired concentration of the final solution. The calculator will then automatically calculate the unknown variable using a specific formula.

Inputting Values

Using an alligation calculator starts with entering the correct values. You must know the concentrations and volumes of both solutions you are mixing.

  1. Find the concentrations of your two solutions. Look for the percentage on the label.
  2. Measure the volume of solution one and then solution two in milliliters (ml). Be as precise as possible.
  3. Choose the desired final concentration for your mixture. Think about what you want to achieve with this solution.
  4. Type these values into the alligation calculator. Use clear numbers and avoid any guesswork. Make sure the concentrations are in the same units.
  5. Enter the first solution's concentration in its designated spot, then do the same for solution two.
  6. Input the desired concentration in its specific field to ensure accuracy.
  7. Check all numbers once more before calculating—mistakes can lead to wrong results.

Practical Examples

Understanding how to use an alligation calculator becomes clearer when looking at practical examples. For instance, suppose you have a 10% ointment and need to dilute it with a 5% ointment to achieve a final concentration of 7%.

Using the alligation calculator, you would input the values for the concentrations of both solutions and find the ratio of parts needed from each solution to produce the desired concentration.

This calculation method can also be applied in scenarios where you need to mix specific volumes of two solutions at different concentrations, such as preparing pediatric dosages or compounding topical medications.

Another practical example arises when needing to create an intermediate concentration by mixing higher and lower concentrated solutions. For instance, if you have Solution A at 20% concentration and Solution B at 5%, using the alligation calculator will help determine how many parts of each solution are required to produce an intermediate concentration of, let's say, 12%.

By entering these values into the tool, pharmacists and pharmacy technicians can efficiently calculate the correct proportions needed without manual trial-and-error methods or complex mathematical equations.


The alligation calculator is an essential tool for pharmacy students and professionals. It simplifies the process of determining the correct proportions of solutions to achieve desired concentrations.

By using this calculator, pharmacists can save time and reduce errors in compounding medications. Its practical benefits make it a valuable asset for day-to-day pharmaceutical calculations.

Mastering its usage can streamline operations and enhance precision in preparing solutions for patients' specific needs.

Frequently Asked Questions

Q: What is alligation calculation?

A: Alligation calculation is a method used in pharmacy and biochemistry to calculate the proportion of two or more ingredients with different concentrations to produce a mixture of a desired concentration.

Q: How is the alligation formula used to solve such problems related to mixtures?

A: The alligation formula is used to find the amount of each solution with different concentrations that needs to be mixed to produce an intermediate concentration.

Q: How is alligation method different from dilution method?

A: Alligation method is used for mixtures with different concentrations to produce an intermediate, while dilution is a simple method of reducing the concentration of a solution by adding solvent.

Q: Can you provide an example of alligation calculation?

A: Sure, for example, if you have a 10% solution and a 25% solution, and you want to mix them to make 100ml of a 15% solution, the alligation method can be used to calculate the quantities of each solution to be mixed.

Q: What are the steps to calculate alligation?

A: The steps to calculate alligation are: 1. Identify the two solutions to be mixed; 2. Assign the lower concentration as Solution 1 and the higher concentration as Solution 2; 3. Enter the values into the alligation formula; 4. Calculate the ratio and individual quantities.

Q: Can you explain the alligation method and its usage in practical scenarios?

A: The alligation method involves mixing two solutions with different concentrations to produce an intermediate concentration. This method is commonly used in pharmacy and biochemistry to prepare solutions of desired strengths.

Q: What is the alligation ratio and how is it calculated?

A: The alligation ratio is the ratio of the parts of the solutions with different concentrations that are mixed to produce the desired concentration. It is calculated using the alligation formula.

Q: How can the alligation calculator be used to perform alligation calculation?

A: The alligation calculator can be used to quickly and accurately calculate the quantities of solutions with different concentrations that need to be mixed to obtain a desired concentration.

Q: What are the key terms related to alligation calculation and their significance?

A: The key terms related to alligation calculation include solution, calculate, mixture, alligation formula, concentration, method, ratio, volume, and example. Understanding these terms is essential for efficient and accurate application of the alligation method.

Q: How does alligation calculation simplify the process of preparing solutions with specific concentrations?

A: Alligation calculation simplifies the process by providing a systematic and efficient method to determine the quantities of solutions with different concentrations that need to be mixed to obtain a desired concentration, saving time and ensuring accuracy.

Leave a Reply

Your email address will not be published. Required fields are marked *