Proportion Calculator

Result

x35
Formula10 × 14 ÷ 4
Ratio b ÷ a2.5
Cross-multiplication check4 × 35 = 140, 10 × 14 = 140

Cross-multiplication in one step

Solves a proportion by cross-multiplication and shows the check, so the answer can be proved rather than trusted.

Proportions are the workhorse of everyday arithmetic. Scaling a recipe from four servings to six, working out paint for a different wall area, converting a map scale into metres — all the same four numbers with one unknown.

The rule is that the product of the outer terms equals the product of the inner ones, so x = b × c ÷ a. The check is printed alongside: both products must match.

What this calculator shows

The value of x and the formula behind it
The scaling factor between the first pair
The cross-multiplication check, where both products must agree

What to keep in mind

The first term cannot be zero, since it is the divisor.
A proportion assumes direct variation; for inverse relationships — more workers, less time — swap the second pair.

FAQs

How do I set a proportion up correctly?

Keep like with like: servings against servings, spoonfuls against spoonfuls. Mixing them gives a meaningless answer even though the arithmetic is right.

What about inverse proportion?

Where one quantity rising makes the other fall — twice the workers, half the time. Then x = a × b ÷ c: the second pair flips.

Can percentages be solved this way?

Yes, and reliably. "15 percent of 2,400" is the proportion 100 : 2400 = 15 : x, giving 360. Many people find that clearer than the formula.

Why show the check line?

To catch a typo. If the outer and inner products disagree, something was mistyped. A correct solution always makes them equal.

Worked example

Scaling a recipe

Input: 4 : 10 = 14 : x

Output: x = 35

Note: If four servings need ten spoonfuls, fourteen servings need thirty-five. Check: 4 × 35 = 140 and 10 × 14 = 140.

Useful links

All tools in Math & Statistics

Proportion Calculator

Result

Related tools

Ratio Calculator

Percentage Calculator

Recipe scaler: adjust ingredients for more or fewer servings

Useful links