Ratio Calculator
Calculate unknowns in ratios, simplify ratios, and find ratio rates instantly
Features
Three ratio calculations on one screen
Handle unknowns, simplified ratios, and ratio rates all together
Automatic calculation as you type
Results appear instantly when you enter numbers—no execute button needed
Select decimal places
Choose from 0 to 4 decimal places to adjust result rounding precision
Copy results with one click
Transfer raw values without thousand separators
How to Use
Select the form for your purpose
Choose from three headings: "Find unknown in ratio", "Simplify ratio", or "Ratio rate"
Enter numbers in each field
For ①, leave one field blank and fill the other three. For ② and ③, enter two numbers
Check and copy the result
Read the result that appears as you type, adjust decimal places if needed, and copy
Use Cases
Resizing images and videos
Calculate height when resizing to width 1280 based on original aspect ratio
Scaling recipes and mixtures
Adjust ingredient amounts when scaling a 2-person recipe to 5 people
Resolution aspect ratio
Express resolution like 1920×1080 as 16:9
Check proportional equation homework
Verify answers to textbook proportions
Basic Knowledge
How to solve proportions
In a proportion of the form A:B = C:D, the product of the inner terms (B×C) always equals the product of the outer terms (A×D). Using this relationship, if three of the four numbers are known, the remaining one can be found with the formula: product of diagonal numbers ÷ remaining number.
How to simplify ratios
To reduce a ratio to its simplest integer form, divide both numbers by their greatest common divisor. Since the GCD of 1920 and 1080 is 120, dividing both by 120 gives 16:9.
Difference between ratio, proportion, and percentage
- Ratio (A:B)：A ratio expresses the relationship between two quantities as "16:9". Multiplying or dividing both sides by the same number preserves the relationship.
- Proportion：Proportion is the value itself showing the size of one quantity relative to another, expressed as a decimal without units, like 1080÷1920 = 0.5625.
- Percentage：Percentage is a unit expressing proportion when the base quantity is 100. For 0.5625, it's written as 56.25% with the % symbol.
Safety and Privacy
Runs entirely in your browser
Your input data is processed only within your browser and is never sent externally.
Processing only in your browser
Calculations is processed entirely within your browser, and input data is not sent to any server.
Communications encrypted with HTTPS
Page loading is also encrypted by TLS, and content cannot be read by third parties.
No transmission to third parties
Input content is not sent to external services such as ad networks or trackers.
No automatic saving of results
Numbers you enter and input suggestions are not stored on the server.
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Updates
- update #353
Fractions like "1/2" can now be entered in all input fields of the ratio calculator
- update #256
Ratio Calculator added: Calculate unknowns in proportions, simple integer ratios, and percentages all in one screen
Featured Tools
RAKKOTOOLS is free to use!
Available free of charge for individuals and corporations, commercial and non-commercial use alike.No prior permission or usage application is required. Feel free to use it in various situations.
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Can be used for commercial purposes such as research, calculation, processing, and conversion in business and production.
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Usage guidelinesYou are free to use it for normal purposes. However, use for purposes that violate laws, infringe on third-party rights, impose significant load on the service, or otherwise interfere with service operation is prohibited.
We do not guarantee the accuracy or completeness of information and calculation results obtained from each tool.
This notice is a translation of the original Japanese text. If there is any discrepancy between the translation and the original, the Japanese original takes precedence.