Ratio Calculator
Provide any three values in A : B = C : D to solve for the fourth. See the simplified form, decimal and percentage equivalents, and a visual breakdown of the ratio.
Enter any three values in A : B = C : D. Leave the unknown field blank.
Ratio Scaling Calculator
Grow or shrink a ratio by any factor while keeping the same proportions.
What is a ratio?
A ratio compares two quantities of the same kind. A class with 12 boys and 18 girls has a ratio of 12 : 18, which simplifies to 2 : 3 — for every 2 boys there are 3 girls. A proportion sets two ratios equal, like 3 : 4 = ? : 20; whenever three of the four terms are known, the fourth is fixed. That single idea powers everything on this page: solving for a missing term, simplifying, converting to a decimal or percentage split, and scaling the pair up or down by any factor.
Ratio calculator, piece by piece
Each card matches a feature above — the proportion solver, the simplified form, the decimal/percentage readout, the pie chart, and the separate scaling tool.
Solve a proportion for the missing term
Given three of the four terms in A : B = C : D, cross-multiply to isolate the fourth. Leave any one input blank — the solver picks up which term is missing and rearranges automatically.
Simplify to lowest terms
After solving, both terms are divided by their greatest common factor so the ratio appears in the smallest whole-number form — the same relationship expressed with the shortest labels.
Decimal, percentage split & pie chart
The mini-stats convert your ratio into two more useful readings — the decimal form a÷b : 1 and the part-of-total percentage a÷(a+b). The pie chart and bar make the split visible at a glance.
Scale a ratio up or down
The separate scaling tool multiplies (grow) or divides (shrink) both terms by the same factor. The relationship stays the same — only the raw numbers change, useful for recipes, photo resizing and model building.
Features of this calculator
- Solve A : B = C : D for any missing term
- Automatically simplify the ratio to lowest whole-number terms
- Display the ratio as a decimal (x : 1) and as a percentage split
- Two-slice pie chart and horizontal bar visualization
- Separate scaling tool to grow or shrink a ratio by any factor
- Full step-by-step working using cross-multiplication
Frequently asked questions
+How do I simplify a ratio?
Divide both terms by their greatest common factor. For decimals, first multiply both sides by a power of ten so the terms become whole numbers, then reduce.
+What's the difference between a ratio and a fraction?
A fraction is always part-to-whole (3/4 = three out of four equal parts). A ratio compares any two quantities, so 3 : 4 could mean three cats for every four dogs — the total isn't fixed.
+How do I scale a ratio up or down?
Multiply both terms by the same factor to grow, or divide both by the same factor to shrink. The relationship between the two quantities is preserved.
+Can a ratio have more than two terms?
Yes. Recipes often use ratios like 1 : 2 : 3 (butter : sugar : flour). The same rules apply — divide every term by the shared GCF to simplify.