Mixing Ratio Calculator
Find the ratio needed to blend two like-for-like solution strengths into one target value. Use it for percentages, molarity, ppm, or any other linearly mixed strength values when you want a practical blend ratio and optional batch amounts.
Edited by Gail Joyce
This calculator page is maintained by the Chemistry Calculators editorial team. The blend-ratio method, ratio interpretation, and worked examples on this page are reviewed against standard solution-preparation methods and commonly used classroom and pharmacy reference material before major updates.
Mixing Ratio Calculator
Enter two source strengths and one target strength to get the blending ratio. Add an optional total batch amount if you want actual quantities as well as parts.
Scope: use like-for-like inputs only. If one value is a percent, all values should be percent. If one value is molarity, all values should be molarity. This page does not work for pH or other non-linear properties.
How to Use the Mixing Ratio Calculator
Use the same order you would use in a lab notebook or pharmacy worksheet: identify the stronger source, identify the weaker source, choose a target between them, and then scale the parts if you need a real batch size.
Enter two like-for-like source strengths
Use the same basis for both sources and the target, such as all percent values, all molarity values, or all ppm values.
Set a target between the two sources
The target must fall between the stronger and weaker values. If it does not, these two sources cannot produce that target by simple mixing.
Read the ratio in parts
The result tells you how many parts of the stronger source to mix with how many parts of the weaker source for the target blend.
Optionally scale to a batch amount
Enter a total amount if you want actual volumes or masses. The calculator will convert the parts into real component quantities.
Table of Contents
Quickly jump to the key sections of this guide.
Understanding Mixing Ratios
A mixing ratio tells you how many parts of one source to combine with another source to reach a target strength. On this page, the goal is practical two-source blend planning: find the parts, then scale them into real amounts if needed.
This approach is useful when the property mixes linearly, such as percentage strength, molarity, ppm, or mass concentration. It is not appropriate for logarithmic properties such as pH or for cases where density or chemical reaction changes the basis of the numbers.
When it works well
Use it for solution prep, stock blending, ppm dilution, and other like-for-like concentration problems where the target sits between two sources.
When not to use it
Do not use it for pH, titration curves, density-driven mass-volume conversions, or mixtures where the target is outside the range of the two source values.
Formulas and Equations
Alligation Ratio
Parts of weaker source = |stronger source - Target|
This cross-difference method returns the parts of each source required to reach the target value. You can simplify the parts to a cleaner ratio and scale them to any batch size.
Scaling to a Total Amount
Once you know the ratio, multiply each share by the fraction of the total amount you want to prepare.
Worked Examples
These examples show how to interpret the ratio and convert it into actual blend amounts when needed.
Example 1: 100% and water to make 50%
Stronger source = 100, weaker source = 0, target = 50.
Parts of stronger source = |50 - 0| = 50
Parts of weaker source = |100 - 50| = 50
Answer: Ratio = 1:1. For 200 mL total, use 100 mL of each source.
Example 2: 30% and 5% to make 15%
Parts of 30% source = |15 - 5| = 10
Parts of 5% source = |30 - 15| = 15
Answer: Ratio = 10:15 = 2:3. For 500 mL total, use 200 mL of the 30% source and 300 mL of the 5% source.
Example 3: 10% and 70% to make 25%
Parts of 70% source = |25 - 10| = 15
Parts of 10% source = |70 - 25| = 45
Answer: Ratio = 15:45 = 1:3. For 1 liter total, use 250 mL of the 70% source and 750 mL of the 10% source.
Common Mistakes
Most blending errors come from mixing unlike units or reversing how the parts are read. These checks keep the ratio usable in real prep work.
Mixing unlike units
Do not combine percent with molarity, ppm with percent, or mass basis with volume basis unless you convert them first.
Choosing a target outside the source range
Two-source mixing can only create a target that lies between the stronger and weaker source values.
Using it for pH or other non-linear properties
This blend-ratio method assumes linear mixing. It does not apply to logarithmic scales such as pH.
Forgetting to scale the parts
A ratio only tells you relative parts. If you need a real batch size, convert those parts into actual amounts using the total amount.
Frequently Asked Questions (FAQs)
These are the main questions people ask when using a two-source blending calculator.
What does the ratio mean?
The ratio tells you how many parts of the stronger source to combine with how many parts of the weaker source. You can scale those parts to any total batch amount.
Does the target have to be between the two sources?
Yes. If the target is outside the two source values, these two sources alone cannot produce that blend by simple mixing.
Can I use any unit?
You can use any unit that mixes linearly, but all three values must use the same basis, such as all percent, all molarity, or all ppm.
What if the ratio contains decimals?
Simplify the ratio to clean parts. The calculator already reduces the ratio so it is easier to scale or communicate.
Can I use this for more than two sources?
This page is for two-source blending only. For more than two sources, use a weighted-average workflow or a broader alligation-style tool instead.
How do I verify the result?
Check the weighted average: final value = (source A amount × source A value + source B amount × source B value) / total amount. It should match your target.
References
For more on blend ratios, two-source solution prep, and classroom solution methods, these references are a stronger starting point than generic web summaries.
| Resource | Description |
|---|---|
| StatPearls: Pharmacy Calculations | Reference material covering concentration, dosing, and blend-ratio work in practical pharmacy calculations. |
| OpenStax Chemistry 2e | Textbook-style support for concentration, solution prep, and weighted-average reasoning. |
| Ansel, H. C., et al. Pharmaceutical Calculations | Standard compounding and ratio-calculation reference used in pharmacy education. |