Ratio Calculator
Please provide any three values below to calculate the fourth in the ratio A : B = C : D.
Ratio Scaling Calculator
What is Ratio?
A ratio is a quantitative relationship between two numbers that describes how many times one value can contain another. Applications of ratios are ubiquitous, and the concept is quite intuitive — it could likely be demonstrated by giving a child half as many cookies as his sister. While the child may not be able to voice the injustice using ratios, the raucous protests that would most likely ensue should make it immediately obvious that he is well aware he has received 1:2 as many cookies as his sister, conceptually, if not mathematically.
Ratios are often expressed as two numbers separated by a colon. They can also be written as "1 to 2" or as a fraction ½. The ratio represents the number that the denominator must be multiplied by in order to yield the numerator — in this case, ½. This is clearer when the first number is larger than the second: with the ratio 2:1, 2 can contain 1 exactly 2 times. It is also possible to have ratios with more than two terms.
Ratios appear in many daily applications: aspect ratios for screens, maps and models described as scaled-down versions of their actual size, baking and cooking, the odds of something occurring, and rates in finance. If, for example, a person wanted to make 5 cakes, each requiring a 1:2:3 ratio of butter:sugar:flour, and wanted the total amounts needed, it would be simple to compute from the ratio: increasing the ratio by five times yields a 5:10:15 ratio of parts, which can then be multiplied by the actual amount per part in the recipe.
Typical Aspect Ratios and Sizes of Screens and Videos
The aspect ratio is the ratio of a geometric shape's sizes in different dimensions — for a rectangle, the ratio of its width to its height. Aspect ratios are used in applications such as tire sizing, paper sizing, and standard photographic print sizes, but some of their most frequent uses involve computer screen dimensions, mobile phone screens, and video sizes. Below is a list of typical computer screen and video resolutions and their aspect ratios.
| Name | Aspect ratio | Width (pixel) | Height (pixel) |
|---|---|---|---|
| 480p | 3:2 | 720 | 480 |
| 576p | 5:4 | 720 | 576 |
| 720p | 16:9 | 1280 | 720 |
| 1080p | 16:9 | 1920 | 1080 |
| 2160p (4K UHD) | 16:9 | 3840 | 2160 |
| 4320p (8K UHD) | 16:9 | 7680 | 4320 |
| 8640p | 16:9 | 15360 | 8640 |
| SVGA | 4:3 | 800 | 600 |
| WSVGA | ~17:10 | 1024 | 600 |
| XGA | 4:3 | 1024 | 768 |
| XGA+ | 4:3 | 1152 | 864 |
| WXGA | 16:9 | 1280 | 720 |
| WXGA | 5:3 | 1280 | 768 |
| WXGA | 16:10 | 1280 | 800 |
| SXGA (UVGA) | 4:3 | 1280 | 960 |
| SXGA | 5:4 | 1280 | 1024 |
| HD | ~16:9 | 1360 | 768 |
| HD | ~16:9 | 1366 | 768 |
| SXGA+ | 4:3 | 1400 | 1050 |
| WXGA+ | 16:10 | 1440 | 900 |
| HD+ | 16:9 | 1600 | 900 |
| UXGA | 4:3 | 1600 | 1200 |
| WSXGA+ | 16:10 | 1680 | 1050 |
| FHD | 16:9 | 1920 | 1080 |
| WUXGA | 16:10 | 1920 | 1200 |
| QWXGA | 16:9 | 2048 | 1152 |
| WQHD | 16:9 | 2560 | 1440 |
| WQXGA | 16:10 | 2560 | 1600 |
Frequently Asked Questions
How do you solve for the missing value in a proportion?
In the proportion A:B = C:D, the cross-products are equal (A × D = B × C), so any one value follows from the other three: D = B × C / A, A = B × C / D, B = A × D / C, and C = A × D / B. For example, 3:4 = 600:D gives D = 4 × 600 / 3 = 800.
How do you simplify a ratio?
Divide both terms by their greatest common factor. For example, 600:800 divides by 200 to give 3:4. Ratios can also be written in the normalized forms 1:n (divide both terms by the first) or n:1 (divide both terms by the second).
What is the difference between enlarging and shrinking a ratio?
Enlarging multiplies both terms by the scale factor, shrinking divides both terms by it. Either way the relationship between the terms is unchanged: 250:280 shrunk 2.5 times is 100:112, the same ratio in smaller numbers.
What is an aspect ratio?
An aspect ratio compares a shape's sizes in different dimensions — for a screen, its width to its height. Most modern screens and videos use 16:9, so a 1920×1080 display and a 3840×2160 (4K) display have the same shape at different sizes.