Scale Recipes, Solve Proportions, Simplify Ratios
Your recipe calls for 6 eggs and serves 4 people. You’ve got 10 guests coming. How many eggs? If you set up the proportion 4:6 = 10:?, cross-multiplication gives you 15. That’s what this tool does, but without the pencil scratch paper.
Two modes here. Proportion solver: give it three numbers and it finds the fourth. Ratio simplifier: give it two numbers like 24:36 and it reduces to 2:3 by dividing both by their GCD (which is 12 in this case).
Where Proportions Show Up
Cooking. This is the big one. You’re doubling a recipe, or cutting it in half, or scaling it to serve 7 instead of 4. The math is simple but easy to mess up when you’re also preheating the oven and the onions are about to burn.
Construction. Concrete mixing ratios (1:2:3 for cement, sand, gravel). Blueprint scales. You’ve got a drawing at 1:50 scale and need to know what 3.2 cm on paper means in real life. That’s 160 cm.
Finance. Debt-to-equity ratios, price-to-earnings, current ratio, business analysis lives on proportions. Simplifying a ratio like 450:600 to 3:4 makes it immediately readable for a presentation.
Chemistry. Stoichiometric calculations are fundamentally proportion problems. If 2 moles of hydrogen react with 1 mole of oxygen, how many moles of hydrogen do you need for 3.5 moles of oxygen?
How It Works Internally
For proportions: if A:B = C:D, then A x D = B x C. Give the tool any three values and it solves for the missing one via simple algebraic rearrangement.
For simplification: it finds the Greatest Common Divisor of both numbers and divides each by it. 24:36 → GCD is 12 → 2:3. Decimals work too.
The GCD & LCM Calculator shows you the step-by-step Euclidean algorithm if you want to understand how the GCD gets computed. The Percentage Calculator is useful when you need to express a ratio as a percentage instead. Everything runs in your browser, nothing leaves your machine.