Math and measurement tools
Ratio Calculator
Simplify a two-part ratio, scale it to a new first value and see each part as a percentage of the whole. Supports positive decimals with clear worked examples.
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How to use this tool
1. Enter the first and second parts of your ratio using the same units. Both values must be greater than zero.
2. Enter the new first part to find the matching second part. For image sizes, use width as the first part and height as the second.
3. Calculate to see the simplest integer ratio, matching second part, scale factor and shares of the combined total.
How simplification and scaling work
The decimal inputs are scaled to whole numbers and divided by their greatest common divisor. Scaling keeps B/A constant: the matching second part is the new first part × B ÷ A. Shares use A/(A+B) and B/(A+B).
Worked example
1920 : 1080 simplifies to 16 : 9. A new first part of 1280 gives a matching second part of 720. The first part is approximately 64% of the combined total; this percentage is not the aspect ratio.
Questions and assumptions
Scope and precision
Use positive values up to 1,000,000 with at most six decimal places. Zero, negative values, scientific notation and multi-part ratios are not supported. Simplification is exact for accepted decimal inputs; scaled outputs show up to ten significant digits.
Applying a ratio
The output is a mathematical proportion. When adapting recipes, physical models or images, rounding and task-specific constraints may require adjustments. Scaling two linear dimensions changes area by the square of the scale factor.
Sources and further reading
Built and maintained by Custom Logic. Page updated .