Ratio & Proportion Finder
Find the missing term in any ratio instantly.
Ratio & Proportion Finder
D = C x (B / A)
Calculated instantly
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What This Calculator Does
The Ratio & Proportion Finder solves proportions of the form A:B = C:D. Given three known terms it instantly returns the missing fourth, which makes it ideal for scaling recipes, resizing images, mixing solutions, and converting between units.
How It Works
A proportion states that two ratios are equal. Cross-multiplying gives A x D = B x C, so the missing value is D = C x B / A. The tool also reports the scale factor, which is how many times larger the matched side has been scaled.
Example
A paint mix needs a 2:5 ratio of base to pigment. If you pour 8 liters of base, the missing pigment is 8 x 5 / 2 = 20 liters.
Formula
D = C × (B / A)From the equality A:B = C:D via cross-multiplication.
Scale = C / AHow many times larger the matched side is scaled.
Reading the Results
Missing Value (D)
The fourth term that keeps the ratio proportional. For A:B = 2:5 with C = 8, the result is 20.
Scale Factor
The multiplier connecting the two ratio sides. It shows how much larger the second set of terms is than the first.
Frequently Asked Questions
What does A:B = C:D mean?
It states that the relationship between A and B is the same as the relationship between C and D. Given any three values, the fourth can always be found.
Can I use this to scale recipes?
Yes. Set A to the original yield and C to the desired yield, with B as the ingredient amount. The result D is the scaled ingredient amount.
What if the ratio is inverted?
Enter the terms in the order they appear in your ratio. Swapping A and B simply gives the reciprocal relationship.