Ratio Calculator
Simplify ratios, find missing values in proportions, and scale dimensions. Includes common aspect ratio presets (16:9, 4:3, 1:1, 21:9) for digital designers and developers.
Ratio
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Simplified Ratio
16 : 9
= 1.777778
Proportion
18
D = 18 (32 : 18)
Aspect Ratio Visual Reference
16:9
HD Video / Widescreen
4:3
Standard Screen
1:1
Square
21:9
Ultrawide
3:2
Photo (35mm)
8:5
16:10 Display
9:16
Portrait Phone
2:3
Portrait Photo
4:5
Instagram Portrait
5:4
Medium Format
Cross-Multiplication
A : B = C : D → A × D = B × C
Enter A, B, and either C or D. The calculator solves for the missing value automatically.
The Formula
A proportion states that two ratios are equal. Cross-multiplication (A × D = B × C) allows solving for any missing term. This is fundamental in scaling, unit conversion, recipe adjustments, and maintaining aspect ratios.
Variable Definitions
First Ratio
The known ratio. Typically the model ratio or desired proportion (e.g., 16:9 for widescreen). A and B are the two quantities being compared.
Second Ratio
The equivalent ratio with one unknown value to solve for. Enter C and leave D blank (or vice versa) to solve the proportion.
Decimal Ratio
A divided by B. The numeric value of the ratio. For 16:9, the decimal ratio is 16/9 ≈ 1.778.
How to Use This Calculator
- 1
Enter values A and B for the first ratio (these are required).
- 2
Enter either C or D (leave the other blank) to solve for the missing value in the proportion A:B = C:D.
- 3
Use the preset dropdown for common aspect ratios: 16:9 (HD video), 4:3 (standard), 1:1 (square), 21:9 (ultrawide), and more.
- 4
View the simplified ratio in its smallest integer form, the decimal ratio (A/B), and the fraction form.
- 5
If both C and D are provided, the calculator checks whether the ratios are proportional.
A proportion states that two ratios are equal; cross-multiplication solves for the missing term
Understanding the Concept
Ratios and proportions are everywhere: aspect ratios for screens (16:9, 4:3), recipe scaling (double a recipe while maintaining ingredient proportions), map scales (1:100,000 means 1 cm on the map equals 1 km in reality), unit conversion (miles to kilometers), and financial ratios (price-to-earnings ratio). A ratio A:B compares two quantities by division. A proportion states that two ratios are equal: A:B = C:D, which is equivalent to A/B = C/D. Cross-multiplication (A × D = B × C) makes solving for any missing term straightforward. Simplifying a ratio by dividing by the GCD gives the smallest integer representation. For example, the ratio 32:18 simplifies to 16:9 (dividing both by 2). The decimal form of a ratio (A/B) is useful for comparison — the aspect ratio 16:9 gives the decimal 1.778, meaning the width is 1.778 times the height. The built-in preset dropdown provides common aspect ratios for media production, photography, and design, making it easy to calculate scaled dimensions without remembering the exact numbers.
Frequently Asked Questions
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