Ratio Calculator
Reduce a ratio to lowest terms, or solve a proportion for the one value you are missing.
Calculation
Ratio
Enter two positive numbers. Decimals like 2.5 are scaled to whole numbers before reducing.
Simplified ratio
Everything is calculated in your browser. Nothing is uploaded.
How to calculate a ratio
Choose a mode
Pick Simplify to reduce a single ratio, or Solve a proportion to fill in a missing value across two equal ratios.
Enter your numbers
Type the two values to simplify, or in solve mode fill three of the four fields and leave the one you want to find blank.
Read the result
The answer updates as you type, showing the reduced ratio or the solved value alongside the completed proportion.
Copy the answer
Click the copy button to put the reduced ratio or the finished proportion on your clipboard.
Why use this tool
Reduce to lowest terms
Enter a ratio like 1920:1080 and get it reduced to its simplest whole-number form, 16:9, by dividing both sides by their greatest common divisor.
Solve a proportion
Set up A:B = C:D, leave one of the four values blank, and the tool cross-multiplies to find the missing number.
Decimals welcome
Values with decimals are scaled to whole numbers before reducing, so 2.5:5 becomes 1:2 and 1.5:2 becomes 3:4.
Instant, no run button
Every change recalculates immediately, so you see the reduced ratio or the solved value the moment you type.
Guards the tricky cases
Empty fields, zero, and division by zero are caught with a clear message instead of a broken or blank result.
Runs entirely in your browser
Every calculation happens on your device. Nothing you type is uploaded.
About this tool
A ratio compares two quantities, and this calculator handles the two jobs that come up most. In simplify mode, type a ratio such as 1920:1080 and it is reduced to lowest terms, 16:9, by dividing both sides by their greatest common divisor. Decimal inputs work too: 2.5:5 is scaled to whole numbers first, then reduced to 1:2. Alongside the reduced ratio you get the decimal value and the normalized 1:n form.
In solve mode you work with a proportion, two equal ratios written A:B = C:D. Fill in any three of the four values and leave the one you want to find blank. The calculator cross-multiplies to solve for the missing number, so 3:4 = 9:? returns 12. This is the everyday tool for scaling a recipe, converting map distances, adjusting a mix, or resizing while keeping proportions. If all four fields are filled it instead checks whether the two ratios are actually equal.
Everything runs in your browser and updates the moment you change a value, so there is no button to press and nothing is sent anywhere. Empty fields, zeros, and division by zero are handled with a plain message rather than a broken answer. For screen and image proportions specifically, the aspect ratio calculator solves a missing width or height, and the percentage calculator covers the closely related job of parts per hundred.
Frequently asked questions
- How do I simplify a ratio?
- Choose Simplify and enter the two values. The calculator divides both by their greatest common divisor to give the lowest-terms form, so 1920:1080 becomes 16:9. It also shows the decimal value and the normalized 1:n form.
- How does solving a proportion work?
- In solve mode you enter a proportion A:B = C:D and leave exactly one field blank. The tool cross-multiplies the three known values to find the fourth, so 3:4 = 9:? returns 12. Fill all four fields and it checks whether the ratios are equal instead.
- Can I use decimals or negative numbers?
- Decimals are supported in both modes; a ratio like 2.5:5 is scaled to whole numbers and reduced to 1:2. Simplify expects positive values, while solve accepts any numbers, including negatives, and reports when a result cannot exist.
- What happens if I divide by zero or leave a field empty?
- The tool checks for these cases. If a solve would require dividing by zero, or if the inputs are empty or not numbers, it shows a short message and no answer rather than displaying an invalid result.
- Is my data uploaded anywhere?
- No. Everything runs in your browser; nothing is sent to a server.
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