Proportion Calculator

Solve proportions and find the missing value in a ratio equation.

x (solved)

20.0000

a/b = c/x

Proportion3/5 = 12/x
Cross Multiply3 * x = 5 * 12
x20.0000

Use the Proportion Calculator above to calculate your results. Enter your values and see instant results — all calculations run in your browser.

Disclaimer: This calculator is for informational purposes only and does not constitute tax, financial, or legal advice. Results are estimates based on the information you provide and current rates. Always consult a qualified tax professional or financial advisor for advice specific to your situation.

How It Works

Our Proportion Calculator helps you quickly solve for an unknown value in a proportion, a fundamental concept in mathematics and real-world applications. Understanding proportions is crucial for scaling recipes, converting units, or even analyzing economic trends. For instance, knowing the proportion of electric vehicles sold in 2026 (projected to be around 25% of new car sales globally, up from 15% in 2023) can help predict future infrastructure needs.

A proportion states that two ratios are equal: a/b = c/d. To solve for an unknown, say 'x', in a proportion like 3/5 = x/10, we use cross-multiplication. This means multiplying the numerator of one ratio by the denominator of the other, setting them equal, and then isolating the unknown variable.

When using the calculator, ensure your units are consistent across the ratios. A common mistake is mixing units (e.g., comparing inches to centimeters directly without conversion). Also, remember that dividing by zero is undefined, so ensure your denominators are never zero.

Example: Budgeting for a 2026 Marketing Campaign

  1. 1 A company plans to spend $75,000 on digital advertising in 2026 if their total marketing budget is $150,000. If their total marketing budget increases to $200,000, how much should they allocate to digital advertising to maintain the same proportion?
  2. 2 We set up the proportion: $75,000 / $150,000 = x / $200,000. Cross-multiplying gives us $75,000 * $200,000 = $150,000 * x. This simplifies to $15,000,000,000 = $150,000 * x.
  3. 3 Dividing both sides by $150,000, we find x = $100,000.
  4. 4 Therefore, to maintain the same proportion of digital advertising within their increased marketing budget, the company should allocate $100,000 to digital advertising in 2026.

Source: Khan Academy · Last updated: April 2026

Frequently Asked Questions

How do I solve a proportion for a missing value?
In the proportion a/b = c/d, cross-multiply to get a*d = b*c, then solve for the unknown. For example, if 3/4 = x/20, then 3*20 = 4*x, so 60 = 4x, and x = 15.
What is the difference between a ratio and a proportion?
A ratio compares two quantities (3:4). A proportion is an equation stating that two ratios are equal (3:4 = 6:8). Proportions are used to solve for unknown values when two quantities maintain a constant ratio.
How are proportions used in real life?
Proportions are used in recipe scaling, map reading, converting units, calculating dosages, resizing images, mixing solutions, and any situation where you need to maintain a constant relationship between two quantities at different scales.

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