Proportion & Ratio Calculator
Solve a : b = c : x, simplify ratios and split an amount by a ratio
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Finds the missing value in A : B = C : D, simplifies ratios and splits an amount by a ratio: for scaling a recipe, sharing a cost or checking an aspect ratio.
How to use
- Under "Solve A : B = C : D", enter the three known values and leave the unknown box empty to get its value and the working.
- Under "Simplify a ratio", type terms such as 12:18 to get the "Simplest whole-number ratio". Decimals and three or more terms work.
- Under "Split by a ratio", enter the "Total to split" and a ratio to get each part. Switch on "Whole numbers only" for whole units.
- Under "Screen and photo aspect ratio", enter the width and height in pixels; "Find the other side for a ratio" gives the missing side for a ratio such as 16:9.
How it works
- The outer product equals the inner product (A × D = B × C), so D = B × C ÷ A.
- With all four boxes filled, the tool says whether the proportion holds. Cases that would divide by zero are not solved.
- With "Whole numbers only", leftover units go to the parts with the largest fractions, so the parts add up exactly to the total.
Questions and answers
- How do I solve a proportion for x?
- Cross multiply: the outer product equals the inner product. If 4 : 200 = 6 : x, then 4 × x = 200 × 6, so x = 300.
- What is 12:18 in simplest form?
- Divide both terms by their greatest common factor, 6, to get 2:3. Decimals such as 1.5:2.5 are first made whole, giving 3:5.
- How do I split 100,000 in the ratio 1:2:3?
- Divide the total by the sum of the terms, 6, and multiply by each term: about 16,667, 33,333 and 50,000. With "Whole numbers only" they add up to exactly 100,000.
- What aspect ratio is 1920 × 1080?
- 16:9. At a width of 1280, a 16:9 picture is 1280 × 9 ÷ 16 = 720 high.