The solver keeps integers, terminating decimals, and fractions as reduced rational numbers. That means an input such as 1/3 stays exact through the calculation instead of becoming a rounded decimal too early. Everything runs locally in your browser.
Private browser utility / Calculators
Proportion Calculator
Runs entirely in your browser - no upload, no sign-up.
Enter an equal-ratio equation
Fill three terms and leave one blank or type x. Fill all four to check the proportion.
Use integers, decimals, or fractions such as 3/4. The bottom terms b and d cannot be zero.
Enter three values and leave one blank to solve it, or enter all four to check the ratios.
What is a proportion calculator?
A proportion calculator finds one missing value in two equal ratios, written a/b = c/d. Enter any three terms to get an exact answer, a decimal, and the cross multiplication steps. Enter all four terms to check whether the ratios form a true proportion.
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How to use
- 01Place the terms
Write the ratios in the form a/b = c/d and enter each known number in its matching field.
- 02Mark the unknown
Leave one field empty or type x. The solver identifies its position and rearranges the cross multiplication formula.
- 03Read the working
Review the exact answer, decimal value, substitution, and equal cross products.
- 04Check a completed proportion
Enter all four values to test whether a × d equals b × c.
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Who it's for
- Students and teachers can solve or check ratio exercises while seeing each algebra step.
- Cooks and makers can scale ingredient quantities or material mixes without changing their relationship.
- Designers and map readers can find a matching dimension or distance from a known scale.
- Scientists and technicians can calculate an unknown in a direct proportional relationship.
FAQ
Is this proportion calculator free?
Yes. You can solve and verify as many proportions as you need without an account, payment, or download.
Are my proportion values uploaded?
No. The calculation runs in your browser. The numbers you enter are not sent to a server for processing.
What numbers can I enter?
You can use positive or negative integers, decimals, and fractions such as 3/4. Inputs are limited to 36 digits per term to keep calculations quick and readable. The denominator positions b and d cannot be zero.
How do you solve a proportion with cross multiplication?
For a/b = c/d, cross multiply to get a × d = b × c. Then divide both sides by the known factor attached to the missing term. For example, if d is missing, use d = (b × c) / a.
Can the calculator solve for any missing term?
Yes. Leave a, b, c, or d blank. The solver chooses the correct rearrangement for that position, as long as the three known values determine one valid answer.
What is the difference between direct and inverse proportion?
Equal ratios describe direct proportion: both quantities change by the same scale factor. In inverse proportion, one quantity increases while the other decreases so their product stays constant. This calculator solves equal-ratio, direct proportions.
Why does the answer show a fraction and a decimal?
The reduced fraction preserves the exact result, while the decimal is convenient for measurement and comparison. Repeating decimals are rounded to ten places, but the fraction is not rounded.