Proportion Solver
Solve a proportion a/b = c/d for the missing value.
Leave the value you want to find as 0.
Solve any proportion
Proportions state that two ratios are equal, and they are everywhere — scaling a recipe, reading a map, resizing an image. Know any three of the four values and the fourth follows by cross-multiplication.
With 2 is to 3 as 8 is to what, the answer is 12. Enter the three values you know and leave the unknown as zero, and the solver fills it in.
Flexible and private
The calculation runs in your browser, so nothing you enter is uploaded.
Frequently Asked Questions
What is a proportion?
A statement that two ratios are equal, like a is to b as c is to d. Knowing three values gives the fourth.
How do I use it?
Enter three of the four values and leave the unknown as zero; it solves by cross-multiplication.
Where is this used?
Scaling recipes, maps, models, and any situation where two quantities keep the same ratio.
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